WERA77: Managing Invasive Weeds in Wheat

(Multistate Research Coordinating Committee and Information Exchange Group)

Status: Active

Project Menu

SAES-422 Reports

Annual/Termination Reports:

[04/27/2020] [04/17/2021] [05/10/2022] [08/24/2023]

Date of Annual Report: 04/27/2020

Report Information

Annual Meeting Dates: 03/02/2020 - 03/02/2020
Period the Report Covers: 10/01/2018 - 09/30/2019

Participants

Judit Barroso, Oregon State University; judit.barroso@oregonstate.edu
Erik Lehnhoff, New Mexico State University; lehnhoff@nmsu.edu
Steve Young, Utah State University; steve.young@usu.edu
Joan Campbell, University of Idaho; jcampbel@uidaho.edu
Traci Rauch, University of Idaho; trauch@uidaho.edu
Tim Seipel, Montana State University; timothy.seipel@montana.edu
Vipan Kumar, Kansas State University; vkumar@ksu.edu
Misha Manuchehri , Oklahoma State; misha.manuchehri@okstate.edu
Caio Brunharo, Oregon State University; caio.brunharo@okstate.edu
Ian Burke, Washington State University; icburke@wsu.edu

Brief Summary of Minutes

BRIEF SUMMARY OF MINUTES OF ANNUAL MEETING:

We met in Maui, HI at the Hyatt Regency Resort on Monday, March 2, 2020 from 2:00 pm to 4:00 pm, before the annual joint meeting of the Weed Science Society of America/Western Society of Weed Science.

The meeting was initiated with a review of the new, approved WERA 077 Proposal:

New Objectives Discussed
- Integrated Management of downy brome, feral rye, jointed goatgrass, and Italian ryegrass
- Reduce spread of critically important herbicide resistant weed species
- Share information among members of group
- Develop educational programs and disseminate information

Update on Past Discussed Studies:

Feral Rye Project

Objectives = flowering time, seed production, shattering, germination
- Ian has much of the seed collected from group. New graduate student in WA that could assess samples in a beneficial way. If they cannot, seed will go to Vipan and/or Caio? And group can decide on what to do with those feral rye seed collections. Some members showed interest in conducting common garden study to understand the phenotypic differences across the region.

Ideas for Research Following New Objectives:

Aggressor Application Timing in CoAXium Wheat
- Oklahoma and Idaho have documented injury with Fusion variety when Aggressor applied near jointing stage
- Disease interaction? Green bridge? Lodging/stunting/black meristem in Oregon?
- Genomes conferring tolerance. Caio brought up discussion on the underlying mutations responsible for injury. Varieties with mutation on AA BB genome are less resistant and varieties with mutation on AA DD genome are high resistant?
- Misha will send up follow-up email on this topic

Italian Ryegrass Management
- Group 1 and group 2 herbicides are mainly used for ryegrass control in OR, ID, OK—Ever increasing problem of resistance to group 1 and group 2 herbicides
- No-till - one-time moldboard in the fall for burying seeds of Italian ryegrass if environment allows (ID)
- Delay seeding can help in ryegrass control in OK, it may not work for other states
- Increased pyroxasulfone rate along with other actives for ryegrass control in OR
- Resistance to pyroxasulfone does not always equal cross resistance to flufenacet

Downy brome Management
- Main grass problem in WA, MT where no-tillage is widely adopted (>72% no till cropland in MT
- Increasing problem of ALS resistance in downy brome in WA and MT. No resistance to powerflex in OR?
- Ian brought up that glyphosate-resistant downy brome populations now identified in Washington with increased EPSPS gene copies as mechanism of resistance
- Tim brought the discussion on a study in Wyoming by Dan Takeila, who is studying the downy brome seed longevity and persistence in rangeland
- Group like to initiate some regional efforts on downy brome management

Metribuzin and pH
- No issues in PNW
- pH issues driven down use in New Mexico

New Herbicide Resistance
- Downy brome to glyphosate in SE WA? Populations were eradicated?
- Imazamox resistant feral rye (?), not necessarily cross resistant to sulfosulfuron
- ALS-resistant goatgrass in WA and OR, especially imazamox? Some biotypes were also resistant to Osprey

Soil Seedbank Study
- Flowering time, seed production, shattering, germination

Emerging Bromus
- Sterile brome
- Rescuegrass
- Rattail fescue
- True cheat (cross resistant to all ALS)

Seedbank longevity
- Feral rye as target?
- How environments shift seed longevity
- Impact of cultural practices on feral rye seedbank longevity

Other Business:

The 2021 meeting will take place on Monday, March 1, 2021 in Boise, Idaho. Time TBD, but likely at the same 3 PM time.

Vipan Kumar will be collecting the state reports (due 6 weeks from the meeting).

Selection of New Secretary/Chair Elect:

Caio Brunharo volunteered to be the new secretary/chair elect for next year. All the meeting participants agreed. Consequently, next year (2021) Vipan Kumar will organize and conduct the meeting and Caio Brunharo will take notes and file the annual report.

The meeting adjourned at 4:00 pm.

Accomplishments

IDAHO REPORT <div>Joan Campbell, Principle Researcher; Traci Rauch, Senior Research Specialist</div> <div>Plant Science Department, University of Idaho, 875 Perimeter Dr. MS 2333, Moscow, ID 83844-2333; 208-885-7730; <a href="mailto:jcampbel@uidaho.edu">jcampbel@uidaho.edu</a> </div> Objective 1. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 106 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used in our area to control Italian ryegrass. Untreated plants are included from each sample. For 2019, samples screenings are in progress for pyroxasulfone, metolachlor, dimethenamid and flufenacet. No sample is resistant to pyroxasulfone or glyphosate. Pinoxaden resistance is near 65% while pyroxsulam and mesosulfuron resistance is widespread (< 90%). The non-selective group 1 herbicides with resistance includes:  clethodim (15%) < sethoxydim (25%) < quizalofop (80%). Objective 1. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop, and herbicide rotation, have altered the makeup of the population. Objective 2. Results. A winter wheat/Italian ryegrass control study evaluated pyroxasulfone and flufenacet at the highest labeled rates with the following application times:  pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat. Italian ryegrass control was improved with flufenacet versus pyroxasulfone at all timings due to a higher rate of pyroxasulfone. flufenacet did not control Italian ryegrass and is most likely due to a resistant population. This study is being repeated in 2020. Pyroxasulfone combined with mesosulfuron/thiencarbazone alone or with pyrasulfotole/bromoxynil or bromoxynil controlled downy brome 98 to 99% compared to pyroxasulfone alone at 88%. In the greenhouse, Italian ryegrass was planted into dry conditions and sprayed with pyroxasulfone. Pots were irrigated with 0.3 inch of rainfall at 0, 8,15, 22,29, 36, and 43 DAT. Pots with untreated plants were included. The study is arranged as a randomized complete block with 4 replications. At all irrigation timings, no Italian ryegrass plants emerged. Objective 2. Outcomes/Impacts: Pyroxasulfone (group 15) was registered for annual grass control, including Italian ryegrass and rattail fescue, in winter and spring wheat in spring 2014. Pyroxasulfone registration has aided in control of group 1 and 2 resistant Italian ryegrass. Very few herbicides control rattail fescue. Pyroxasulfone and pyroxasulfone/fluthiacet treatments controlled rattail fescue 89-97% in 2018. Winter wheat yield was not reduced by pyroxasulfone when 0.5 inch of sprinkler irrigation was applied immediately after planting and spraying on the same day (worst-case scenario). Wheat had minimal injury in 11 conventional-tilled (chisel plowed/field cultivated) sites and in seven direct-seed locations. U of I studies were instrumental in implementing pyroxasulfone label changes including an increased use rate and a preplant application time in winter wheat. These label changes have aided growers by giving them more options to improve weed efficacy. flufenacet also was registered in wheat fall 2014. Our flufenacet studies were useful to FMC when drafting rates and timings for their label. This information will help growers use these products safely and effectively to control grass weeds with minimal crop injury. These registrations provide needed tools to help control herbicide resistant weeds, especially Italian ryegrass. Objective 3. Results: Three winter wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms October 2019. Pyroxasulfone, dimethenamid, and metolachlor were applied after seeding along with an untreated control. Experimental design was a split plot with herbicide as the main factor and variety with and without safener as the subfactor with four replications. Wheat will be harvested in August 2020. Spring wheat will be planted in 2020 in comparable experiment. Objective 3. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide selection to increase herbicide rotations to combat resistance in the future. Objective 4. Results: A field trial was re-established at UI research farms near Moscow and Genesee to examine tillage effects on rattail fescue. Spring wheat was direct seeded in 2019. The rotation is spring wheat- spring chickpea - winter wheat. Tillage initiated in the fall 2018 included fall disc or chisel plow followed by spring field cultivation. A no-tillage treatment is included as a control. Heavy harrow replaces disc in year 2 and 3. The tillage will be performed all 3 years, 2 years or 1 year for a total of 7 tillage regimes. In 2019, rattail fescue and brome density did not differ among treatments after the first tillage year. Tillage treatments were applied fall 2019 for the second year of the study. Chickpea will be planted spring 2020 and weed numbers and chickpea seed yield will be measured. Objective 4. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control. Tillage is important but research on how invasive and how often is unknown. This data will help growers take an integrated weed management approach to reducing rattail fescue and increasing crop yield. Objective 5. Two new broadleaf herbicides in winter wheat were evaluated. Halauxifen/fluroxypyr was evaluated for prickly lettuce and mayweed chamomile control in winter wheat. Halauxifen/fluroxypyr plus 2,4-D ester controlled prickly lettuce 90% at 80 DAT but did not control mayweed chamomile (79%). Bicyclopyrone/bromoxynil combined with various slow release fertilizers (NDemand 30L, Stand 12-0-2, Maximum N-Pact, CoRoN 28-0-0) did not visibly injure winter or reduce grain yield and test weight compared to the untreated check. Bicyclopyrone/bromoxynil was combined with grass herbicides (imazamox, pyroxsulam, and mesosulfuron/thiencarbazone) that require a urea ammonium nitrate (UAN) fertilizer adjuvant. The bicyclopyrone/bromoxynil label currently does not allow applications with fertilizer. Bicyclopyrone/bromoxynil alone plus UAN and imazamox plus bicyclopyrone/bromoxynil and UAN injured winter wheat 15%. Grain yield and test weight did not differ among treatments. Bicyclopyrone/bromoxynil applied at four growth stages (2 tiller, joint, swollen boot and ¼ head visible) did not visibly injured spring wheat. Grain yield did not differ among treatments including the untreated check. Aggressor herbicide controlled downy brome and feral rye 90% or better in Co-AXium winter wheat. Mesosulfuron/thiencarbazone controlled rattail fescue and suppressed jointed goatgrass. Objective 5. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide resistant weeds. Bicyclopyrone/bromoxynil and halauxifen/fluroxypyr may be options for possible control of herbicide resistant broadleaf weeds. Objective 6. Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage and rate. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. A ventenata sample was screened with 3 herbicides. It was resistant to mesosulfuron and sulfosulfuron (group 2) and susceptible to glyphosate. A jointed goatgrass sample was screened with 3 herbicides. It was resistant to imazamox (group 2) and susceptible to quizalofop and glyphosate. Seven downy brome seed samples were screened with 12 herbicides. No sample was resistant to metribuzin, pyroxasulfone, clethodim, sethoxydim, quizalofop or glyphosate. Samples were resistant to pyroxsulam, imazamox, propoxycarbazone, mesosulfuron, sulfosulfuron, and flucarbazone (group 2). Eight wild oat samples were screened with 9 herbicides. No sample was resistant to sethoxydim, clethodim or glyphosate. Samples were resistant to pyroxsulam, mesosulfuron, imazamox, and quizalofop. Some samples were developing resistance to pinoxaden and pinoxaden/fenoxaprop. A mayweed chamomile seed sample was treated with 4 herbicides. The sample was resistant to thifensulfuron/tribenuron and metsulfuron/thifensulfuron/tribenuron (group 2). It was not resistant to pyrasulfotole/bromoxynil and clopyralid/fluroxypyr. Objective 6. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices. Objective 7. Results: Project personnel participated in cereal schools in north Idaho in January. Research information was presented at the Western Society of Weed Science meeting in March. Cereal research was also presented at other grower meetings in the winter and field days in June and July. Objective 7. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems. OREGON REPORT <div>Judit Barroso, Weed Scientist.</div> <div>Crop and Soil Science Department, Columbia Basin Agricultural Research Center, Oregon State University. (541)2784394. <a href="mailto:judit.barroso@oregonstate.edu">judit.barroso@oregonstate.edu</a></div> Research: Control of kochia (Bassia scoparia), prickly lettuce (Lactuca serriola), and lambsquarter (Chenopodium berlandieri) in wheat. These weed species continue to be problematic and are widespread in the wheat cropping systems of the Pacific Northwest (PNW). The spread of Group 2 herbicide resistance in kochia and prickly lettuce in the region are probably the cause of many of the control problems. The objective of this research was to identify herbicide treatments with different modes of action for management of these species. The herbicides evaluated were three group 4 herbicides including fluroxypyr + halauxifen-methyl (6 fl oz/ac) , clopyralid + fluroxypyr (16 fl oz/ac), and 2,4-D (8 fl oz/ac); two group 2&4 herbicides including pyroxsulam + fluroxypyr (16 fl oz/ac) and florasulam + halauxifen-methyl (0.75 oz/ac); one group 6&27 herbicide containing bromoxynil + pyrasulfotole (13.5 fl oz/ac). A field study was conducted at the OSU Columbia Basin Agricultural Research Center near Pendleton, OR to test the efficacy of these herbicides against broadleaf weeds in spring wheat. The soil at this site is a Walla Walla silt loam. On April 17, 2019, ‘WB6341’ spring wheat was planted with a no-till drill with 10 in row spacing. Treatments were applied on May 31, 2019 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. Crop damage was not significant among treatments throughout the evaluation process. There were no significant differences among sprayed treatments for kochia control. The best results were obtained with pyroxsulam + fluroxypyr with 100% control. Prickly lettuce showed significant differences among treated plots. Bromoxynil + pyrasulfotole provided the best control (100%) followed by the tank mix clopyralid + fluroxypyr with halauxifen-methyl + florasulam (93%), clopyralid + fluroxypyr (88%), and the tank mix of fluroxypyr + halauxifen-methyl with 2,4-D (85%). Fluroxypyr + halauxifen-methyl alone and pyroxsulam + fluroxypyr had the lowest control with 34% and 43%, respectively. Lambsquarter’s control also showed significant differences among sprayed treatments. The tank mix of fluroxypyr + halauxifen-methyl with 2,4-D (100%), the tank mix of clopyralid + fluroxypyr with florasulam + halauxifen-methyl (100%), bromoxynil + pyrasulfotole (100%), and fluroxypyr + halauxifen-methyl (99%) had the highest control followed by pyroxsulam + fluroxypyr (91%) and clopyralid + fluroxypyr (84%). Control of downy brome (Bromus tectorum L.) in winter wheat. Downy brome is probably the most problematic grassy weed in the wheat production systems of the PNW. Group 2 herbicide resistance is widespread in this species making its control sometimes impossible. It is urgent to find chemical options outside of Group 2 herbicides to control downy brome and preserve no-till agriculture. The objective of this research was to explore chemical options to control downy brome without relying only on group 2 herbicides. Two field studies were conducted at the OSU Columbia Basin Agricultural Research Center near Pendleton, OR. Experiment 1 was established to study the control of triallate (group 8), imazamox (group 2), pyroxsulam (group 2), and pyroxasulfone (group 15) and their combinations and experiment 2 was established to study the control of carfentrazone + pyroxasulfone (group 14+15), chlorsulfuron + metsulfuron methyl (group 2), metribuzin (group 5), propoxycarbazone (group 2), and their combinations. The soil at this site is a Walla Walla silt loam. Experiment 1. On October 5, 2018, ‘ORCF 102’ winter wheat was planted with 10 in row spacing. Pre-plant incorporated treatment (triallate) was applied on October 4, 2018. Early post-emergence treatments were applied on November 15, 2018, delayed pre-emergence treatments (pyroxasulfone) were applied on October 30, 2018 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph and late post-emergence treatments were applied on April 24, 2019 using the same mentioned equipment. Downy brome control showed no significant differences among sprayed treatments due to the high variability in the data, ranging from a low of 55% with pyroxasulfone alone to a high of 96% with triallate + imazamox (LPOST) + NIS. Yield did not show any significant difference among treatments, ranging from a low of 57.03 bu/A with pyroxasulfone to a high of 74.40 bu/A with triallate + imazamox (LPOST) + NIS. Although no significant control differences were found, pre-emergence herbicides pyroxasulfone and triallate have shown to improve downy brome control and help to reduce downy brome group 2 resistant populations. Experiment 2. On October 5, 2018, ‘Bobtail’ winter wheat was planted with 10 in row spacing. Treatments were applied with a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. Pre-plant treatments (carfentrazone + pyroxasulfone) were applied on October 4, 2018. Post-plant pre-emergence treatments (carfentrazone + pyroxasulfone with chlorsulfuron + metsulfuron methyl) were applied on October 12, 2018. Very early post treatments (metribuzin and metribuzin with carfentrazone + pyroxasulfone) were applied on November 15, 2018. The post-emergence treatment (propoxycarbazone) was applied on April 22, 2019. Significant differences were observed for downy brome control regarding treatments. Three treatments showed 100% control; carfentrazone + pyroxasulfone 3.5 fl oz/A (pre-plant), carfentrazone + pyroxasulfone 4.5 fl oz/A (pre-plant) and carfentrazone + pyroxasulfone 3.5 fl oz/ac (pre-plant) + carfentrazone + pyroxasulfone 1.0 fl oz/ac (very early post) + Metribuzin 2 oz/ac (very early post). However, these treatments were not different from carfentrazone + pyroxasulfone 2.5 fl oz/A (pre-plant) (82% control), carfentrazone + pyroxasulfone 3.5 oz/ac (post-plant pre-emergence) (75% control), carfentrazone + pyroxasulfone 4.5 oz/ac (post-plant pre-emergence) (76% control), and carfentrazone + pyroxasulfone 3.5 fl oz/ac (post-plant pre-emerge) + Olympus 0.9 oz/ac (very early post) (84% control). The least control was shown by carfentrazone + pyroxasulfone 2.75 fl oz/A (post-plant pre-emerge) (44%), carfentrazone + pyroxasulfone 3.5 fl oz/ac + chlorsulfuron + metsulfuron methyl 0.3 oz/ac (post-plant pre-emerge), carfentrazone + pyroxasulfone 3.5 fl oz/ac + Metribuzin 2 oz/ac (very early post), and with propoxycarbazone 0.9 oz/ac (post-emergence). I want to emphasize that the chemical control of downy brome could have been increased by competition with jointed goatgrass (Aegilops cylindrica) that was the prevalent weed in this trial. The options for pre-emergence herbicides studied (triallate, pyroxasulfone, carfentrazone + pyroxasulfone) and metribuzin in post-emergence have been found to be good alternatives or complement to Group 2 herbicides for downy brome control. Impacts: From an herbicide resistant strategy point of view, it is necessary to provide growers with as many tools as possible to control problematic weeds. This and the previous research provided some chemical options to control these problematic species and help growers make informed decisions. Harvest weed seed control in wheat production systems of the PNW. Harvest weed seed control (HWSC) might perform an important role in controlling problematic weeds, by decreasing the weed seed bank. However, HWSC practices will not be effective if plants have previously shed all or a great part of their seeds before harvest, or if the combine is unable to collect the seed. The objectives of this study were: 1) evaluate the efficacy of chaff collection and chaff plus straw collection to reduce weed infestations and dispersion, 2) evaluate seed production, seed height, and seed retention of important weed species at harvest, and 3) determine the effects of chaff or chaff and straw removal on soil organic matter and moisture content. After two harvest seasons, in three studied farms, the collection of chaff did not produce significant differences in weed infestation compared to the control treatment (no residue removal). The collection of chaff and straw (bale direct system) provided marginally significant Sisymbrium altissimum reduction (10.6% on average) on one of the farms and a reduction tendency in the other farm with this problematic species. Bromus tectorum, Lolium perenne ssp. multiflorum, Vulpia myuros, and Chorispora tenella had an average seed retention at harvest of less than 50%. In addition, the low seed height in V. myuros and C. tenella makes these species poor candidates for HWSC. Sisymbrium altissimum and Secale cereale had average seed retention at harvest greater than 50% and seed height above 30 cm. The efficacy of HWSC practices in the PNW winter wheat cropping systems will be species dependent. While no differences have been found in soil carbon due to chaff or chaff and straw removal compared to the control, the collection of chaff plus straw caused a statistically significant reduction in gravimetric soil moisture (2 mm of precipitation per month) in the top 30 cm of soil. In arid and semi-arid areas, where the soil water accumulation is important, the removal of straw may not be a profitable practice. Impact: We found that the efficacy of HWSC in the PNW is going to be species dependent and harvest time very critical to maximize control. The findings from this research will help growers in their decision to include these practices in their Integrated Weed Management programs depending on their weed issues and economy. These practices have a high potential to improve weed management in wheat production systems in our region, and consequently, their sustainability. OKLAHOMA REPORT Misha Manuchehri, Extension Weed Specialist, Department of Plant and Soil Sciences, Oklahoma State University, 371 Agricultural Hall, Stillwater, OK 74078. 405-744-9588. <a href="mailto:misha.manuchehri@okstate.edu">misha.manuchehri@okstate.edu</a> Identification and Management of ACCase Resistant Italian Ryegrass Pinoxaden resistant Italian ryegrass biotypes were suspected in Oklahoma for many years; however, it wasn’t until last year that resistant populations were confirmed in greenhouse screenings. The use of group 15 herbicides may improve the control of these difficult-to-manage plants. Several studies have been conducted throughout Oklahoma over the past four years to evaluate the use of pyroxasulfone, pyroxasulfone + carfentrazone, and flufenacet+metribuzin on Italian ryegrass management. Control typically is > 90% for treatments that included pyroxasulfone at the delayed preemergence timing. Similar control is achieved with pyroxasulfone + carfentrazone and flufenacet + metribuzin but crop response from metribuzin often is seen; therefore, it is critical that proper rates are used for specific soil types. Timely rains and proper herbicide to soil contact also contributes to the success of these treatments. A current study is evaluating the impact of residue on the performance and crop response of these group 15 herbicides and preliminary results reveal the importance of proper seed bed prep when using mechanical tillage as well as good seed row closure. Impact Have screened thousands of weed biotypes in Oklahoma to aid weed managers in their decision making. From these screenings, we were the first to identify ACCase resistant Italian ryegrass in Oklahoma. With this information herbicide treatments that are not effective can be replaced with new plans that are. Successful ryegrass control can improve Oklahoma wheat yields by at least 20% and reduce grain discounts. Winter Wheat Variety Tolerance to Metribuzin Metribuzin is a herbicide that is still widely used in cropping systems annually. However, its use in winter wheat in Oklahoma has declined due to varietal sensitivity or lack of information regarding the topic. To evaluate modern winter wheat varieties, a trial was conducted at Dacoma, Fort Cobb, Goodwell, and Perkins, Oklahoma in the fall of 2019. Treatments consisted of two herbicide mixtures and a nontreated control. Mixtures included pyroxasulfone at 119 g ai ha-1 plus 105 or 210 g ai ha-1 of metribuzin. Herbicide mixtures were applied preemergence and delayed preemergence (wheat spike). Visual wheat response was recorded every two to three weeks after the first application. Six weeks after application at the Fort Cobb and Perkins locations, biomass from one meter of row was clipped at the soil surface, dried, and recorded. For biomass at Fort Cobb, there was an application timing by metribuzin rate interaction where biomass at the preemergence timing was 40 and 74% less than the nontreated control following metribuzin at 105 and 210 g ai ha-1, respectively. At the delayed preemergence timing, biomass was similar following both rates but was reduced by approximately 31% compared to the nontreated control. For biomass at Perkins, there was a metribuzin rate effect where biomass decreased by 42% and 70% compared to the nontreated control following metribuzin at 105 and 210 g ai ha-1, respectively. Results suggest that variety, application timing, and metribuzin rate will continue to be important when using this herbicide in wheat. Impact Approximately 86% of planted winter wheat acres in Oklahoma are public varieties. Increased information about varietal tolerance to metribuzin will improve relationships between Oklahoma agricultural stakeholders and Oklahoma State University. The use of metribuzin also will add a rarely used herbicide site of action to our list of management strategies to suppress and/or control winter annual grasses and will relieve some selection pressure for resistance from overused ALS and ACCase herbicides. Rescuegrass Management in Winter Wheat Rescuegrass is one of the most challenging winter annual weeds to manage in Oklahoma. There are few conventional herbicides labeled for rescuegrass control in winter wheat and for the ones that are labelled, control is often inconsistent. Products used in herbicide tolerant wheat (Clearfield® and CoAXium®) provide adequate control of rescuegrass; however, overreliance of these systems increases the selection pressure for herbicide resistant weed biotypes. To evaluate integrated management of rescuegrass, a study was conducted at Lahoma, Marshall, and Tipton, Oklahoma and Burkburnett, Texas to assess planting date, wheat variety, and herbicide selection on rescuegrass control. Wheat was planted at an optimal, delayed, and late timing where the early date represented the optimal time to sow wheat harvested for grain. Recently released varieties, Green Hammer and Showdown, were used. Both varieties offer high yield potential; however Showdown brings low competitive ability while Green Hammer offers high competition with advantage in forage yield. Two commonly used herbicides, pyroxsulam at 18.4 g ai ha-1 and sulfosulfuron at 35.2 g ai ha-1, were applied when rescuegrass was at the 2- to 3-leaf stage. At Lahoma, a delay in planting date increased percent visual weed control provided by the two herbicides. At Marshall, the same trend was observed; however, pyroxsulam controlled rescuegrass more than sulfosulfuron by 23%. Additionally, rescuegrass plants were counted for two 0.10 m-2 quadrats per plot. Rescuegrass counts at Marshall decreased by 13 plants per 0.10 m-2 from the optimal to delayed planting date. Overall, a delay in planting date did decrease rescuegrass populations while pyroxsulam and sulfosulfuron are two herbicide options for non-herbicide tolerant wheat that provided between 27 and 51% control in these studies. Impact Have shared identification and management tools for rescuegrass, a winter annual grass weed that is poorly understood in the state and beyond. Wheat fields infested with rescuegrass provide little grain and often are not worth investing chemical weed management dollars into as the plant is highly competitive and responds poorly to herbicides. Our data shares these facts with growers while encouraging them to manage the plant by rotating to a summer crop, using infested fields for primarily forage, or controlling rescuegrass with glyphosate or tillage prior to a delayed planting date. UTAH REPORT <div>Earl Creech, Extension Agronomist</div> <div>Corey Ransom, Extension Weed Scientist</div> <div>Steve Young, Weed Scientist (contact) Plants, Soils & Climate Department, Utah State University, 4820 Old Main, Logan, UT 84322; 435-797-0139; <a href="mailto:steve.young@usu.edu">steve.young@usu.edu</a></div> Research: Kochia-cover crop study – Year 3 (2020) The objective of this study is to evaluate the influence of cover crops, and planting dates and rates on kochia populations in wheat fields of Utah and southern Idaho. Similar to Years 1 (2018) and 2 (2019), planting dates and rates will be assessed as secondary tactics (e.g., early or late season plantings – avoidance, size advantage; high rates – resource use, competitive advantage) against kochia in combination with cover crops as a primary tactic. Wheat allelopathy study – Year 2 (2020) Many plants are reported to naturally produce secondary compounds that can have a deleterious effect on neighboring vegetation, also known as allelopathy. While not lethal, this allelopathic effect by a plant can also provide a competitive advantage against weed species. Unknown is to what extent allelopathy in wheat prohibits species of weeds. Therefore, our hypothesis is that wheat cultivars from the Pacific Northwest will stop weed species seed from germinating. The objective is to determine the allelopathic effect of several wheat cultivars on the growth and development of weed seed. Extension: Kochia-cover crop study – Year 3 (2020) Similar to Years 1 (2018) and 2 (2019), specific methods for disseminating results will include: 1) establishing research at university field sites, 2) conducting field days in partnership with local growers, crop advisors and seed dealers (Utah Seed), 3) updating county educators, regional specialists, and private crop advisors at in-service meetings, 4) uploading findings on university extension and private organization websites, 5) presenting findings at local and regional meetings and conferences, 6) announcing project findings in local newsletters, newspapers for growers, and during statewide and regional speaking engagements, and 7) integrating research findings into course teachings that target next generation ag-professionals. Impacts: Kochia-cover crop study – Year 3 (2020) Outcomes: Growers will benefit from our project through increased understanding and directly implementable results. Kansas Report <div style="text-align: justify;">Vipan Kumar, Weed Scientist</div> <div style="text-align: justify;">Kansas State University, Agricultural Research Center, Hays, KS</div> <div style="text-align: justify;">Phone: 785-625-3425; E-mail: <a href="mailto:vkumar@ksu.edu">vkumar@ksu.edu</a></div> Research: <div>Evaluation of CoAXium® wheat production system for controlling feral rye and downy bromein Kansas.</div> <div>CoAXium® wheat production system is a new non-GMO herbicide-resistant wheat technology that combines the use of Aggressor® (quizalofop-p-ethyl, Group 1) herbicide with wheat varieties containing genes that confer tolerance to this herbicide – AXigen® trait. Three CoAXium® hard red winter wheat varieties (LCS Fusion AX, Crescent AX, and Incline AX) that contain the AXigen® trait (resistance to the ACCase class of herbicides) are now commercially available for use. Two separate field experiments were conducted in Kansas to determine the effectiveness of Aggressor® herbicide rates and timing for control of feral rye and downy brome. An on-farm field study near Great Bend, KS evaluated three different rates (8, 10, 12 fl oz/a) and timings (fall, spring or fall followed by spring) of Aggressor® herbicide for feral rye control in winter wheat during 2018/2019 growing season. The study utilized a CoAXium® winter wheat variety “LCS Fusion AX” planted on Nov. 19, 2018. Fall and spring treatments of Aggressor® were applied on Dec 19, 2018 and April 4, 2019.  The second study near Hays, KS evaluated same Aggressor® treatments on “Incline AX” variety planted on Oct 14, 2018. Fall and spring treatments of Aggressor® herbicides were made on Nov 25, 2018 and April 14, 2019 in Hays. At both locations, all treatments were applied with a CO2-operated backpack sprayer set to deliver 14 gpa at 35 psi at 3 mph. The Great Bend site had natural infestation of downy brome; whereas, the Hays site was artificially infested with downy brome at wheat planting. No visual injury on winter wheat was observed with Aggressor® treatments at both locations. All Aggressor® treatments provided excellent (>94 %) late-season control of feral rye compared to non-treated plots irrespective of application timing and rates used in Great Bend site. Similarly, end-season control of downy brome was excellent (95 to 99%) with all Aggressor® treatments tested. Altogether, these studies indicated that the CoAXium® Wheat Production System can provide effective herbicide option for control of feral rye and downy brome in Kansas wheat production.</div> Control of kochia (Bassia scoparia L.), Tansy mustard (Descurainia pinnata L.) and Henbit (Lamium amplexicaule L.) in winter wheat. Winter and summer annual broadleaf weed species, including tansy mustard, henbit, and kochia are problematic in Kansas winter wheat production. In addition, kochia has developed widespread resistance to ALS inhibitors (group 2) and glyphosate (group 9) herbicides in western Kansas. The purpose of this research was to determine the effectiveness of dichloprop-p (group 4), bromoxynil (Maestro®, group 6), MCPA (Rhonox®, group 4), and fluroxypyr (Comet™, group 4) for control of kochia, tansy mustard, and henbit in winter wheat. All these herbicides were tested in different combination and application rates: dichloprop-p at 8, 12, 16 fl oz/a; Maestro® at 16 and 24 fl oz/a; Rhonox at 4.5 and 9 fl oz/a; Comet at 7.5 and 11 fl oz/a. Field experiment was conducted at Kansas State University Agricultural Research Center in Hays, KS to test these treatments. Treatments were arranged in a randomized complete block design with 4 replications. Soil at the study site was Roxbury silt loam with pH 7.6 and 2.1% organic matter. Winter wheat variety “Joe” was drilled in tilled ground on Oct 3, 2018 at 10-in row spacing using seeding rate of 60 lbs/ac. Herbicide applications were made on April 15, 2019 when winter wheat was 4- to 5-tillers stages. Treatments were applied using a CO2-operated backpack sprayer set to deliver 14 gpa at 40 psi at 3.0 mph. At the time of herbicide applications, kochia was 2 to 3-in tall and, tansy mustard was 10 to 12 in tall and henbit was blooming. No significant crop injury was noticed with any of these tested treatments. Tank-mixed treatments of dichloprop-p + Maestro and dichloprop-p + Maestro + Rhonox at various rates provided effective control (88 to 96%) of tansy mustard and henbit at 45 days after treatments (DAT). Control of these two species ranged from 80 to 87% with sole treatments of dichloprop-p, Maestro, Rhonox, and Comet at 45 DAT. No significant differences were observed among treatments for kochia control and control ranged from 76 to 81% at 45 DAT. On an average, herbicide treatments improved wheat grain yield by 13 to 28% compared to non-treated weedy check plots.   Washington Report <div>Drew J. Lyon and Ian C. Burke</div> <div>Crop and Soil Sciences Department, Washington State University, Pullman, WA 99164-6420; 509-335-2961. <a href="mailto:drew.lyon@wsu.edu">drew.lyon@wsu.edu</a></div> Research: Evaluation of Aggressor herbicide for the control of downy brome in the CoAXium wheat production system. The CoAXium™ wheat production system was recently developed by the Colorado Wheat Research Foundation, Inc., Limagrain Cereal Seeds, LLC and Albaugh, LLC. AXigen™ is the nonGMO trait in wheat that confers tolerance to the ACCase inhibitor (Group 1) herbicide Aggressor ™ (quizalofop-P-ethyl). The AXigen trait will be made available to both private and public breeders and was one of the reasons we were interested in evaluating the system. Aggressor is labelled to control annual grassy weeds, such as downy brome, jointed goatgrass and feral rye that are problematic in the low to intermediate rainfall zones of eastern WA. LCS Fusion AX winter wheat was direct seeded at the Cochran Farm near Walla Walla, WA. The soil at this site is a Ritzville silt loam. Postemergence treatments were applied on April 4th with a CO2-powered backpack sprayer set to deliver 15 gpa at 47 psi at 1.5 mph. The wheat growth stage was from 3 to 8 tiller and beginning to grow upright. Downy brome pressure was very high, with an average of 430 plants per square meter, and most of the plants were tillered. The level of downy brome control between the three rates of Aggressor evaulated was not significantly different. Downy brome control with Aggressor was not influenced by the addition of NIS, MVO or UAN. On the April 30th rating date, 26 days after application, all Aggressor treatments were providing greater than 95% control of downy brome. On the same rating date, Osprey and PowerFlex HL were providing approximately 50% control. On the final rating date, June 6th, all Aggressor treatments were providing outstanding control of downy brome, whereas Osprey and PowerFlex HL essentially were providing no control. Downy brome resistance to Group 2 herbicides like Osprey, PowerFlex HL, Beyond, and Outrider is common in the Walla Walla area. This trial demonstrated the effectiveness of the CoAXium Wheat Production System for the control of downy brome. However, overuse of this new technology is likely to quickly result in selection of downy brome biotypes resistant to the active ingredient, quizalofop-P. Evaluation of Axial Bold for wild oat control in spring wheat. A field study was conducted near Pullman, WA to evaluate crop safety and wild oat control with Axial Bold. Axial Bold is a premixture of pinoxaden and fenoxaprop. Both active ingredients are ACCase inhibitors (Group 1). The study area followed winter wheat. Soil at this site is a Palouse silt loam with 4.2% organic matter and a pH of 5.0. On May 28th, treatments were applied with a CO2-powered backpack sprayer set to deliver 10 gpa at 49 psi at 2.3 mph. Wheat was at the two tiller stage and was 12 inches tall. Wild oat plants were 3 inches tall and there were an average of 12 plants per square meter.In general, group 1 herbicides including Axial Bold, Axial XL, Tacoma 1EC and Discover NG, provided better control than group 2 herbicides including Everest 3.0, Olympus and OpenSky. None of the treatments provided commercially acceptable (> 80%) control. Axial Bold was the only treatment to come close to this level of control. Olympus- and OpenSky-treated plots yielded similarly to the nontreated check plots. Yield was increased by all other treatments when compared to the nontreated check. No crop injury was observed with any of the treatments in this study. Some wild oat populations in Washington, including the population in this study, are now resistant to Axial. Axial has helped to keep wild oat under control for many years, but as this study demonstrates, our ability to control wild oat with Axial is diminishing. The addition of fenoxaprop to pinoxaden (Axial Bold) provides some additional control of wild oat, but it may be insufficient for the control of populations already resistant to Axial. Germination response of downy brome, wild oat, and Italian ryegrass to gibberellic acid in Palouse silt loam. Downy brome (Bromus tectorum L.), Italian ryegrass (Lolium multiflorium) and wild oat (Avena fatua L.) currently plague the dryland wheat production systems of the Pacific Northwest (PNW). Each of these grass species dominate in distinct climatic zones. Downy brome, a winter annual, is common in the low to intermediate rainfall zones. Italian ryegrass also a winter annual, and wild oat, a summer annual, invades in high rainfall zones. Gibberellic acid (GA3), is a naturally occurring plant growth hormone that can be used alleviate seed dormancy, as well as modifying flowering, germination, and senescence processes. A greenhouse study was conducted to access the response of new and old seed of the three grass species to GA3 (RyzUp Smartgrass) in Palouse Silt Loam soil. Treatments of GA3 (1.4, 14, 28, 56 g ai ha -1) were applied to the prepared soil surface and immediately incorporated with approximately 0.25 cm of water. A negative control (0 g ai ha-1) and a positive control (GA3 soak) were included. Seedling germination was assessed at 1, 2, and 3 WAT. At 4 WAT final counts were recorded, and aboveground biomass was harvested. Treatment and age of seed significantly (P <0.001) affected the response downy brome counts 4 WAT. Italian ryegrass counts at 4 WAT were significantly (P <.0150) impacted by both treatment number and age of seed. Wild oat germination was not affected by GA3 applications, but by age of seed - older seed resulted in more plants than new seed. Based on this data, GA3 could be used as an effective management tool for newly seeded downy brome and Italian ryegrass seedbanks in dryland wheat production systems of the PNW.

Publications

Barroso, J., D.J. Lyon, and T. Prather. 2019. Russian thistle management in a wheat-fallow crop rotation. (PNW492). Beaudoin, M. R., R. J. Zuger, and I. C. Burke. 2020. Germination response of downy brome, wild oat, and Italian ryegrass       to gibberellic acid in Palouse silt loam. Weed Sci. Soc. Am. Abst 60:160. Lyon, D.J., M.E. Thorne, P. Jha, V. Kumar, and T. Waters. 2019. Volunteer buckwheat control in wheat. Crop Forage    Turfgrass Manage. doi:10.2134/cftm2019.05.0033. Kerbs, B.D., A.G. Hulting, and D.J. Lyon. 2019. Scouringrush (Equisetum spp.) control in dryland winter wheat. Weed       Technol. 33:808-814. Lyon, D. J, Walsh, M. J., Barroso, J, Campbell J. M., and A. G. Hulting. 2019. Harvest Weed Seed Control:   Applications for PNW Wheat Production Systems. PNW 730. p. 10. Raiyemo, D. A., J. M. Campbell, R. Ma, W. J. Price, T. A. Rauch, and T. S. Prather. 2019. Safener may enhance   tolerance to soil-applied herbicide for winter wheat varieties grown in the Pacific Northwest. Weed        Science Society of America Proceedings. http://wssaabstracts.com/public/59/proceedings.html. Rauch, T., and J. Campbell. 2019. Broadleaf weed control in wheat with halauxifen plus florasulam. Western       Society of Weed Science Proceedings 72:30. Kumar, V., R. Liu, and D.E. Peterson. 2019. Management of feral rye with CoAXium wheat production system       in Kansas. K-State Agronomy eUpdates (published on Oct 11, 2019). <a href="https://webapp.agron.ksu.edu/agr_social/article_new/management-of-feral-rye-with-coaxium-wheat-">https://webapp.agron.ksu.edu/agr_social/article_new/management-of-feral-rye-with-coaxium-wheat-</a>     production-system-in-kansas-357

Impact Statements

Washington: A new Herbicide Resistant Weeds Map allows growers to see the results of the weeds screening program by county. Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

Date of Annual Report: 04/17/2021

Report Information

Annual Meeting Dates: 03/01/2021 - 03/01/2021
Period the Report Covers: 10/01/2019 - 09/30/2020

Participants

Drew Lyon - Washington State University - drew.lyon@wsu.edu;
Judit Barroso - Oregon State University - judit.barroso@oregonstate.edu;
Joan Campbell - University of Idaho - jcampbel@uidaho.edu;
Cody Creech - University of Nebraska - ccreech2@unl.edu;
Mithila Jugulam - Kansas State University - mithila@ksu.edu;
Vipan Kumar - Kansas State University - vkumar@ksu.edu;
Misha Manucherhri - Oklahoma State University - misha.manuchehri@okstate.edu;
Timothy Seipel - Montana State University - timothy.seipel@montana.edu;;
Lovreet Shergill - Montana State University - lovreet.shergill@montana.edu;
Philip Westra - Colorado State University - Philip.westra@colostate.edu;
Eric Westra - Colorado State University - epwestra.rams.colostate.edu;
Caio Brunharo - Oregon State University - caio.brunharo@oregonstate.edu;
Ian Burke - Washington State University - icburke@wsu.edu;
Scot Hulbert - Washington State University - scot_hulbert@wsu.edu

Brief Summary of Minutes

Project No. and Title: WERA-77

Managing Invasive Weeds in Wheat
Period Covered: 10-2019 to 09-2020
Date of Report: 04/17/2021
Annual Meeting Dates: 03-01-2020 to 03-04-2020

Selection of New Secretary/Chair Elect:

Lovreet Shergill volunteered to be the new secretary/chair elect for next year. All the meeting participants agreed. Consequently, next year (2022) Caio Brunharo will organize and conduct the meeting and Lovreet Shergill will take notes and file the annual report.

The meeting was conducted on March 1, 8-9am.

Kansas Report Vipan Kumar Research:
Evaluation of Anthem Flex application timings for downy brome (Bromus tectorum) and blue mustard (Chorispora tenella) control in winter wheat. A field study was conducted at Kansas State University Agricultural Research Center near Hays, KS in 2019/2020 growing season to determine the effectiveness of Anthem Flex herbicide rates and application timings for control of downy brome and blue mustard. Study site was planted with a winter wheat variety ‘Joe’ on Oct 3, 2019 using 60 lbs/a seeding rate. The study evaluated Anthem Flex at 2.5, 3.25, and 3.5 fl oz/a as preplant and preemergence (PRE) timings as well as in sequential application at 3.25 fl oz/a followed by a POST application of Olympus at 0.6 oz/a. In addition, a tank-mixture of Anthem Flex at 2.8 fl oz/a plus Finesse at 0.4 oz/a applied delayed PRE (DPRE) was also tested.

Herbicide treatments for preplant, PRE, DPRE and POST timings were applied on Sep 29, Oct 7, Oct 11 and Nov 19, 2019, respectively. All treatments were applied with a CO2-operated backpack sprayer set to deliver 14 GPA at 35 psi at 3 mph. The study site had natural infestation of downy brome and blue mustard. Data on winter wheat injury, percent visible control of downy brome and blue mustard were collected. No visual injury on winter wheat was observed with Anthem Flex treatments tested across all rates and timings. Irrespective of application timing and rates, all Anthem Flex treatments provided excellent, late-season control of downy brome (92 to 99%) and blue mustard (95 to 99%) compared to non-treated plots. Reduced interference of downy brome and blue mustard by Anthem Flex-based treatments resulted in wheat grain yields of 50 to 60 bu/a, as compared to nontreated plots (18 bu/a). In conclusion, these results suggest that the Anthem Flex applied at 2.5 to 3.5 fl oz/a rate in preplant, PRE, or delayed PRE timings can provide an effective control of downy brome and blue mustard in dryland winter wheat in western Kansas.

Response of feral rye (Secale cereal L.) populations from Kansas wheat fields to Aggressor™ and Beyond® herbicides. Feral rye is one of the most troublesome winter annual grass weed species in Kansas winter wheat production. Two herbicide-tolerant wheat production systems, viz. CoAXium® winter wheat (resistant to quizalofop-p-ethyl) and Clearfield® winter wheat (resistant to imazamox) are currently available for selective control of winter annual grass weed species, including feral rye. However, there is lack of information on the response of feral rye populations from Kansas wheat fields to Beyond® (imazamox) and Aggressor™ (quizalofop) herbicides. Seeds of about eight different feral rye populations were collected in 2020 from four different counties in north central Kansas at the time of wheat harvest. Greenhouse experiments were conducted at Kansas State University Agricultural Research Center in Hays, KS, to determine the response of those populations to increasing doses of Beyond® and Aggressor™ herbicides. Feral seedlings from each population were grown in 4-inch squared plastic pots containing commercial potting mixture. Experiments were conducted in randomized complete block (blocked by population) design with 12 replications. Beyond® herbicide doses of 0, 1.25, 2.5, 5, 10, and 20 fl oz/a and Aggressor™ herbicide doses of 0, 2, 4, 8, 16, and 32 fl oz/a were separately tested on each feral rye population. All Beyond® doses included methylated seed oil (MSO) at 1% v/v and Aggressor™ doses included nonionic surfactant (NIS) at 0.25% v/v. All herbicide doses were applied when feral rye seedlings reached 2 to 4-lf stage in a cabinet spray chamber. Data on shoot dry weights were collected at 21 days after treatment (DAT) and analyzed using 3-parameter log-logistic model in R software. Based on dose-response analysis, the estimated GR90 values for Beyond® herbicide (the dose needed for 90% reduction in shoot dry weights) ranged from 8.2 to 41.4 fl oz/a (wide variation in response to Beyond® herbicide); whereas, the estimated GR90 values for Aggressor™ herbicide ranged from 7.5 to 14.7 fl oz/a among the tested populations. Based on these results, it can be concluded that the tested feral rye populations will not be controlled with the labelled field-use rate of Beyond® herbicide (5 fl oz/a), but should be controlled by a field-use rate (10 to 12 fl oz/a) of Aggressor™ herbicide.

Impact Statement: These research findings were shared with Kansas wheat growers through a numerous presentations and popular press articles on Kansas Agricultural Experiment Station Research Reports (https://newprairiepress.org/kaesrr/vol6/iss5/23/). Results were also shared with wheat growers, county ag agents and crop consultants through Weed Schools, Crop Pest Management Webinar, and Cover Your Acres conference conducted across western Kansas in fall of 2020 or spring 2021.

Washington Report

Drew J. Lyon and Ian C. Burke
Research:
Evaluation of Avadex® Microactiv™ herbicide for the control of downy brome and Italian ryegrass. The objectives of this study were twofold: 1) Determine the level of control that Avadex MicroActiv (Group 8) provides against downy brome and Italian ryegrass in a direct seed winter wheat production system, and 2) Ascertain if the combination of Avadex MicroActiv with either Zidua (Group 15), Zidua + Sencor (Group 5), Beyond (Group 2) or PowerFlex HL (Group 2) provides better grass weed control than the products applied individually. The soil at this site is an Athena silt loam with 2.9% organic matter and a pH of 5.2. Winter wheat was the previous crop. The field was sprayed with glyphosate on October 6, 2019 and Avadex MicroActiv was applied with a 50 ft Valmar applicator on October 7th at 15 lb/A to half of the trial area. Two, 50 ft by 200 ft strips received Avadex MicroActiv and two strips did not.

Herbicide treatments were randomized and replicated four times within the respective strips. On October 8th, the trial area received 0.47 inch of rainfall that aided in the activation and incorporation of the Avadex MicroActiv. Mechanical incorporation of the Avadex MicroActiv occurred at planting on October 10th with a Horsch high disturbance direct-seed drill with paired rows on a 15-inch row spacing. The cultivar UI Magic CL+ was seeded at a depth of 1.5 inches and a rate of 110 lb seed/acre. Zidua and Zidua + Sencor preemergence treatments were applied on October 11th with a CO2-powered backpack sprayer. Beyond and PowerFlex HL were applied postemergence in the fall (November 18, 2019) and in the late winter (February 28, 2020). On November 18, 2019 there was an average of 24 annual grass plants per square foot in the four, nontreated check plots. None of the herbicides applied caused any crop injury. Avadex MicroActiv and Zidua each provided some control of downy brome and Italian ryegrass. Avadex MicroActiv provided slightly better downy brome control, whereas Zidua provided slightly better Italian ryegrass control. Neither product provided commercially acceptable control of either annual grass weed when applied alone. The combination of Avadex MicroActiv plus Zidua provided the best control of downy brome and Italian rygrass and increased yield by 18 bu/A when compared to the nontreated check. The addition of Sencor to Zidua did not increase the control of either annual grass weed when compared to Zidua alone or in combination with Avadex MicroActiv. The group 2 herbicides (Beyond and PowerFlex HL) provided very little control of either downy brome or Italian ryegrass when applied on their own. However, when combining Beyond or PowerFlex HL with Avadex MicroActiv, downy brome control was better than Italian ryegrass control. This study demonstrated that as resistance to the postemergence Group 2 herbicides increases in both downy brome and Italian ryegrass, it will be important to use preplant and preemergence herbicides with at least two different sites of action to control these two troublesome annual grass weeds in wheat.

Management of downy brome in the Pacific Northwest (PNW) has become more challenging due to the emergence of triazine, ALS-inhibitor, ACCase-inhibitor and glyphosate resistant genotypes. One potential method to manage herbicide resistant downy brome would be evolutionary theory-based methods aiming to reduce the reproductive fitness of downy brome by changing the cropping systems sufficiently to select against the various genotypes known to be present in the PNW. To develop evolutionary based methods, we must know how much adaptive traits vary across the region and within fields so the potential response to evolutionary management methods can be modeled. Full-Sib families were grown in two greenhouses with 3 replications in each greenhouse, after 53 days of vernalization. Number of tillers, height (cm), days until visible panicle, and days until first ripe seed were measured. The percent of total variability explained by a trait was calculated using mixed models to perform an analysis of variance. The percent of the phenotypic variability explained by the Full-sib families varied by trait ranging from 24.1% for days to first ripe seed to 80.3% for first visible panicle. Number of tillers and height, both traits thought to be plastic had 65.2% and 32.5%. The only large effect that was not attributed to the full-sib families was the height trait, where it accounted for 28.2% of the total variation present. The Full-sib Family was a significant random effect in all traits.

Because large amounts of heritable variation in adaptive traits is present, it is likely that genotype by location interactions could maintain genetic variation if migration is present. Reducing migration of downy brome seed may limit the amount of genetic/phenotypic adaptation within fields thus the effectiveness of alternative management methods such as mowing or crop rotation may be improved. Equipment shared between fields/locations should be cleaned thoroughly after use to prevent the maintenance of genetic/phenotypic variation in downy brome in PNW wheat.

Impact Statement: Grower and industry awareness of herbicide resistance continued to increase in 2020 through a variety of presentations and articles in the popular press and through Timely Topic posts, the Weeders of the West Blog, and WSU Wheat Beat Podcast episodes on the Wheat and Small Grains Website (smallgrains.wsu.edu). Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

IDAHO REPORT

Joan Campbell Research:
Objective 1. Results. A study established in the fall 2019 in CoAXium ‘Fusion’ winter wheat examined a possible interaction between Aggressor (quizalofop) herbicide application timing and eyespot disease. No disease was present this year. Lodging occurred from late applications timings of Aggressor (2 node stage which is off label).

Objective 1. Outcomes/Impacts. Understanding the CoAXium system helps aid our growers to obtain the highest grain quality and yield while also controlling difficult annual grass weeds.

Objective 2. Results. A winter wheat/Italian ryegrass control study evaluated pyroxasulfone and pyroxasulfone/carfentrazone at the highest labeled rates with the following application times: pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat.
Italian ryegrass control at the pre-fertilization timing was less than all other application timings. Italian ryegrass control was improved with pyroxasulfone/carfentrazone versus pyroxasulfone at all timings due to a higher rate of pyroxasulfone. Axiom did not control Italian ryegrass and is most likely due to a resistant population. This study is being repeated in 2021.

In other trials, pyroxasulfone combined with mesosulfuron/thiencarbazone alone or with pyrosulfotole/bromoxynil controlled downy brome 89 to 92% compared to pyroxasulfone alone at 76%. Pyroxasulfone/flumioxazin or pyroxasulfone/flumioxazin/metribuzin controlled downy brome 90% or better and did not injure winter wheat.

Objective 2. Outcomes/Impacts: Pyroxasulfone (group 15) was registered for annual grass control, including Italian ryegrass and rattail fescue, in winter and spring wheat in spring 2014. Pyroxasulfone registration has aided in control of group 1 and 2 resistant Italian ryegrass. Very few herbicides control rattail fescue. Pyroxasulfone treatments controlled rattail fescue 89-97% in 2018.Winter wheat yield was not reduced by pyroxasulfone when 0.5 inch of sprinkler irrigation was applied immediately after planting and spraying on the same day (worst-case scenario). Wheat had minimal injury in 11 conventional-tilled (chisel plowed/field cultivated) sites and in seven direct-seed locations. U of I studies were instrumental in implementing pyroxasulfone label changes including an increased use rate and a preplant application time in winter wheat. These label changes have aided growers by giving them more options to improve weed efficacy. Pyroxasulfone/carfentrazone also was registered in wheat fall 2014. Our pyroxasulfone/carfentrazone studies were useful to FMC when drafting rates and timings for their label. This information will help growers use these products safely and effectively to control grass weeds with minimal crop injury. These registrations provide needed tools to help control herbicide resistant weeds, especially Italian ryegrass.

Objective 3. Results: Castle CL, Magic CL, and Sparrow winter wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms October 2019. Pyroxasulfone, dimethenamid, and metolachlor were applied after seeding along with an untreated control. Experimental design was a split plot with herbicide as the main factor and variety with and without safener as the subfactor with four replications. dimethenamid and metolachlor herbicides applied at a 3X rate postplant preemergence caused substantial injury and yield reduction to Sparrow and Magic CL winter wheat varieties at one location. Yield was increased with safener. Castle CL showed a level of inherent tolerance. Pyroxasulfone applied at a 3X rate did not cause visual injury at either location. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms spring 2020. Pyroxasulfone, dimethenamid, and metolachlor were applied after seeding along with an untreated control. Experimental design was a split plot with herbicide as the main factor and variety with and without safener as the subfactor with four replications.
No spring wheat variety was visibly injured by dimethenamid, metolachlor or Pyroxasulfone at a 2X rate applied postplant preemergence at two locations. Metolachlor and dimethenamid resulted in a 5 to 7% yield reduction.

Objective 3. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass, windgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide mode of action to aid herbicide resistant weed management in wheat.

Objective 4. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 106 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used to control Italian ryegrass. Untreated plants are included from each sample. Due to limited greenhouse space, samples screenings are in progress for pyroxasulfone, metolachlor, dimethenamid and Axiom. No sample is resistant to pyroxasulfone or glyphosate. Pinoxaden resistance is 74% while pyroxsulam and mesosulfuron resistance is widespread 89 and 90%, respectively. The non-selective group 1 herbicides with resistance includes: clethodim (23%) < sethoxydim (57%) < quizalofop (77%).

Objective 4. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop and herbicide rotation, have altered the makeup of the population.

Objective 5. Results: A field trial was re-established at UI research farms near Moscow and Genesee to examine tillage effects on rattail fescue. Chickpea was direct-seeded spring 2020. The rotation is spring wheat- spring chickpea - winter wheat. Tillage initiated in the fall 2018 included fall disc or chisel plow followed by spring field cultivation. A no-tillage treatment is included as a control. Heavy harrow replaces disc in year 2 and 3. The tillage is performed all 3 years, 2 years or 1 year for a total of 7 tillage regimes. In 2020, rattail fescue in chickpea was higher in the direct seed treatment. Winter wheat was planted fall 2020 and weed numbers and wheat yield will be measured.

Objective 5. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control in direct seed. Tillage is important but research on how invasive and how often is unknown. This data will help growers take an integrated weed management approach to reducing rattail fescue and increasing crop yield.

Objective 6. Results: Three new broadleaf herbicides in winter wheat were evaluated. pyrosulfotole/bromoxynil FX (pyrasulfotole/bromoxynil/fluroxypyr) and WideARmatch (fluroxypyr/clopyralid/halauxifen) provide good mayweed chamomile control at 95 and 99%, respectively. Pixxaro (fluroxypyr/halauxifen) plus 2,4-D also controlled mayweed chamomile 94% at 70 DAT. Talinor applied to winter wheat combined with mesosulfuron/thiencarbazone and fungicides did not reduce yield compared to the untreated check.

Objective 6. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide resistant weeds. Talinor, WideARmatch, and Pixxaro may be options for possible control of herbicide resistant broadleaf weeds.

Objective 7. Results: Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. Three interrupted windgrass samples were screened to 5 herbicides. All samples were resistant to imazamox, mesosulfuron, pyroxsulam (group 2) and susceptible to pyroxasulfone and glyphosate. Two downy brome seed samples were screened with 8 herbicides. Samples were susceptible to metribuzin, pyroxasulfone, quizalofop or glyphosate. Samples were resistant to pyroxsulam, imazamox, propoxycarbazone, and mesosulfuron (group 2). A kochia sample was screened to 5 herbicides. It was susceptible to saflufenacil, dicamba, fluroxypyr, and glyphosate and was resistant to imazamox (group 2).

Objective 7. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices.

Objective 8. Results: Project personnel participated in cereal schools in north Idaho in January. Research information was presented at the Weed Science Society of America/Western Society of Weed Science joint meetings in March. Cereal research was also presented at other grower meetings in February and in-person field day in June.

Objective 8. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems.

OKLAHOMA REPORT

Misha Manuchehri Research:
Tillage System Impact on Efficacy of Delayed Preemergence Herbicides in Winter Wheat.

Delayed PRE herbicides can provide season-long Italian ryegrass (Lolium perenne L. ssp.
multiflorum (Lam.) Husnot) control in Oklahoma winter wheat when applied at proper rates and successfully incorporated. However, heavy previous crop residue found in reduced tillage systems may reduce efficacy. Some herbicide labels describe this, and producer sentiments echo it. A study was conducted during the 2019-20 and 2020-21 seasons near Stillwater, Oklahoma to evaluate the efficacy of delayed PRE herbicides in no-till, conservation, and conventional wheat tillage systems. Conservation tillage was comprised of a single pass of a sweep plow set approximately 10 cm below the soil surface with a rotary hoe following behind. The conventional tillage system was disked twice with a tandem disk prior to planting. Plots were maintained weed free throughout the summer fallow period with burndown herbicide applications as needed. Herbicide treatments consisted of metribuzin, pinoxaden, pyroxasulfone, and/or pyroxasulfone + carfentrazone-ethyl applied alone or in tank-mixture. No tillage by herbicide interaction was observed for visual crop injury, weed control, or wheat yield.

Significant crop injury for pyroxasulfone + metribuzin was observed in 2019. No visual crop injury was noted in 2020, likely due to delayed rains. In both years, ryegrass control greater than 92% was achieved following treatments of pyroxasulfone + metribuzin and pyroxasulfone + pinoxaden. Soil surface residue as influenced by tillage did not affect the efficacy of delayed PRE herbicides in winter wheat. With a wide range of tillage systems across Oklahoma, these results may influence use of PRE herbicides moving forward.

Winter Wheat Variety Tolerance to Metribuzin. Metribuzin is a herbicide that is still widely used in cropping systems annually. However, its use in winter wheat in Oklahoma has declined due to varietal sensitivity or lack of information regarding the topic. To evaluate modern winter wheat varieties, a trial was conducted at Fort Cobb and Perkins, Oklahoma in the fall of 2019. Winter wheat varieties Fusion AX, Showdown, Strad CL Plus, and Uncharted were evaluated. Treatments consisted of two herbicide tank mixtures and a nontreated control. Mixtures included pyroxasulfone at 119 g ai ha-1 plus 105 or 210 g ai ha-1 of metribuzin. Herbicide mixtures were applied PRE or delayed PRE (wheat spike). Visual wheat response, biomass, and crop yield were recorded. For biomass collected between 4 and 6 weeks after planting at Fort Cobb and Perkins, there was a metribuzin rate main effect where compared to the nontreated control, biomass decreased by 40% and 42% at 105 g ai ha-1 and 74% and 70% at 210 g ai ha-1, respectively. Fort Cobb derived a time by rate interaction for yield where the high rate applied PRE displayed reduction. For Perkins, a yield by rate by variety interaction occurred where Strad CL Plus showed a significant reduction between all treatments, Fusion AX and Uncharted showed a yield reduction at the high rate, and Showdown exhibited no yield reduction across all treatments.

Results suggest that proper application rate in accordance to soil type and characteristics is important, crop application timing is crucial, and variety tolerant selection is imperative.

Rescuegrass Management in Winter Wheat. Rescuegrass (Bromus catharticus) is an early emerging winter annual grass weed prevalent in winter wheat production of the southern Great Plains. Growers can successfully manage rescuegrass in herbicide tolerant wheat systems; however, control in non-herbicide tolerant wheat often is poor. To evaluate integrated management of rescuegrass and other Bromus spp., a study was conducted at Marshall and Lahoma, Oklahoma and Burkburnett, Texas to assess an early, mid-, and late planting date, one high-competitive and one low-competitive wheat variety, and two common herbicides: sulfosulfuron at 35.2 g ai ha-1 and pyroxsulam at 18.4 g ai ha-1. The earliest date represented optimal sowing window for grain only wheat production. At Marshall, mid- and late planting dates decreased rescuegrass biomass 19 and 23 g per 0.25 m-2, respectively, compared to the early planting date. At Burkburnett, a reduction in downy brome (Bromus tectorum) biomass was observed for the late planting date, reducing biomass by 28 and 37.6 g more than mid or early date, respectively. Pyroxsulam controlled rescuegrass best at Marshall by decreasing biomass 28 g more than sulfosulfuron. Although, sulfosulfuron had better control at Burkburnett by decreasing rescuegrass biomass 5.5 g more than nontreated. True cheat (Bromus secalinus L.) and downy brome biomass decreased 98% after both pyroxsulam and sulfosulfuron treatments at Lahoma. Treatments of pyroxsulam or sulfosulfuron and a delay in planting by two to six weeks after the early sowing time did provide a reduction in rescuegrass biomass.

Impacts

Group 15 herbicides are currently the only chemical tool to manage Italian ryegrass in Oklahoma winter wheat. According to our research, when using a carrier volume of at least 15 gallons per acre, tillage system, likely will not impact ryegrass control.

Approximately 86% of planted winter wheat acres in Oklahoma are public varieties. Increased information about varietal tolerance to metribuzin will improve relationships between Oklahoma agricultural stakeholders and Oklahoma State University. The use of metribuzin also will add a rarely used herbicide site of action to our list of management strategies to suppress and/or control winter annual grasses and will relieve some selection pressure for resistance from overused ALS and ACCase herbicides.

Have shared identification and management tools for rescuegrass, a winter annual grass weed that is poorly understood in the state and beyond. Wheat fields infested with rescuegrass provide little grain and often are not worth investing chemical weed management dollars into as the plant is highly competitive and responds poorly to herbicides. Our data shares these facts with growers while encouraging them to manage the plant by rotating to a summer crop, using infested fields for primarily forage, or controlling rescuegrass with glyphosate or tillage prior to a delayed planting date.

OREGON REPORT

Judit Barroso Research:
Control of prickly lettuce (Lactuca serriola) and lambsquarter (Chenopodium berlandieri) in spring wheat. In a continuing effort to find herbicides with different modes of action active on problem species, such as prickly lettuce and lambsquarter in wheat, we conducted this experiment at the Columbia Basin Agricultural Research Center in 2020. The herbicides tested were pre-tank mixes of fluroxypyr + halauxifen-methyl (both group 4), fluroxypyr + clopyralid + halauxifen-methyl (all group 4), fluroxypyr + pyroxsulam (groups 4 and 2), bromoxynil + pyrasulfotole (groups 6 and 27), and tank mixes of fluroxypyr + halauxifen-methyl with 2, 4-D (group 4), fluroxypyr + halauxifen-methyl with and thifensulfuron-methyl (group 2), fluroxypyr + clopyralid + halauxifen-methyl with 2,4-D, fluroxypyr + clopyralid + halauxifen-methyl with thifensulfuron-methyl, and fluroxypyr + clopyralid with halauxifen-methyl + florasulam (groups 4 and 2). The experiment was a complete randomization block design with four repetitions. The crop was seeded with a conventional drill with 7.5 inch row spacing. Treatments were applied on May 27, 2020 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. The wheat ranged from 2-5 tillers to in the boot stage and was 2 feet tall at the time of application. Prickly lettuce was 7-9 leaves and 5-10 inches tall. Lambsquarter was 4-10 shoots and 4-12 inches tall. Weed control was evaluated at two, six, and eight weeks after treatment using a visual evaluation from 0 to 100, with zero indicating no control and 100 complete control. Prickly lettuce showed significant differences among treated plots for all three evaluation dates. On the final evaluation date, fluroxypyr + clopyralid + halauxifen-methyl with 2,4-D and bromoxynil + pyrasulfotole had the highest control at 100%, which was not significantly different from fluroxypyr + clopyralid + halauxifen-methyl with thifensulfuron- methyl, fluroxypyr + clopyralid with halauxifen-methyl + florasulam, fluroxypyr + clopyralid + halauxifen-methyl, fluroxypyr + halauxifen-methyl with 2, 4-D with a control higher than 96%. Fluroxypyr + clopyralid with thifensulfuron-methyl and fluroxypyr + pyroxsulam show slightly lower control but close to 90% and fluroxypyr + clopyralid showed the least control at 84%.

Lambsquarter did not show significant differences among sprayed treatments on any of the three evaluation dates, ranging from 99-100% control.

Impacts: We are providing growers with information on prickly lettuce and lambsquarter control using herbicides with different modes of action (MOA). This study will help them to design integrated weed control strategies that prevent the development of resistant populations.

Improve Russian thistle (Salsola tragus) management in wheat cropping systems.

a) Effect of row spacing and seeding rate on Russian thistle in spring barley and spring wheat.
Russian thistle is a persistent post-harvest issue in the semi-arid region of Pacific Northwest (PNW). Farmers need more integrated management strategies to control it. Russian thistle emergence, mortality, plant biomass, seed production, and crop yield were evaluated in spring wheat and spring barley planted in 18- or 36-cm row spacing and seeded at 73 or 140 kg ha−1 in Pendleton and Moro, Oregon, during 2018 and 2019. Russian thistle emergence was lower, and mortality was higher in spring barley than in spring wheat. However, little to no effect of row spacing or seeding rate was observed on Russian thistle emergence or mortality in both years. Russian thistle seed production and plant biomass followed crop productivity; higher crop yield produced higher Russian thistle biomass and seed production and lower crop yield produced lower weed biomass and seed production. Crop yield with Russian thistle pressure was improved in 2018 with 18-cm rows or by seeding at 140 kg ha−1 while no effect was observed in 2019.

Increasing seeding rates or planting spring crops in narrow rows may be effective at increasing yield in low rainfall years of the PNW, such as in 2018. No effect may be observed in years with higher rainfall than normal, such as in 2019.

Impacts: A good crop is necessary to suppress Russian thistle germination and reduce its density during the growing season. Spring barley has shown to be more competitive than spring wheat to suppress Russian thistle. In the semi-arid region of the PNW, including spring barley over spring wheat is recommended to suppress Russian thistle. Increasing seeding rates or planting spring crops in narrow rows may be effective in low rainfall years but no effect may be observed in years with higher rainfall than normal.

a) Evaluation of different herbicides and adjuvants, and application time to improve post- harvest Russian thistle chemical control. Two trials, one in Pendleton, OR and one in Moro, OR, were established to evaluate several post-emergence herbicides with different adjuvant options (Tables 1) to control Russian thistle in fallow and post-harvest. The herbicides studied were Gly Star® Plus (glyphosate), Sharpen® (saflufenacil), Deadbolt® (bromoxynil + 2,4-D), Brox®-M (bromoxynil), Huskie® (bromoxynil + pyrosulfotole) and Starane® NXT (bromoxynil + fluroxypyr). The adjuvants studied were In-Place® (Drift control agent), Fire-Zone® (Methylated Seed Oil (MSO)), ExuroTM (MSO), Accudrop® (Drift control agent + deposition aid + surfactant), and Hell-Fire®(Herbicide activator). Russian thistle seeds were sprinkled in the experimental area right before seeding to secure a uniform infestation. The trials were a split-plot complete randomized block design with four repetitions, where the main plot (10 ft x 40 ft) was the chemical treatment and the sub-plot (10 ft x 20 ft) was the application time (in the first 2 days after harvest (DAH) and in two weeks after harvest (WAT)). Treatments were conducted with a CO2-powered backpack sprayer delivering 15 gal/A. Visual weed control assessments were performed 3 and 6 weeks after treatment (WAT) to evaluate herbicide and adjuvant efficacy. In both sites, treatments improved Russian thistle control when they were sprayed 2 WAH compared to 2 DAH (Table 1). This may be due to the plants having extra time to regrow after harvest, therefore having more surface area to be treated and/or growing more actively. Gly Star Plus treatments and Huskie treatment were least affected by the spray time. There was not significant difference among the adjuvants applied with Gly Star Plus or Sharpen.

In Pendleton, on the final evaluation date for the 2 DAH application, all four Gly Star Plus treatments, as well as the Huskie treatment, showed Russian thistle control of 94-100%. The remaining treatments, including all Sharpen treatments, Deadbolt, Brox-M, and Starane NXT, showed varying degrees of significant difference ranging from 53-100%. On the final evaluation date for the application at 2 WAH, all Sharpen treatments, Deadbolt, and Starane NXT treatments showed similar control to Gly Star Plus and Huskie treatments. Brox-M showed the lowest Russian thistle control among sprayed treatments.
In Moro, on the final evaluation date for the 2 DAH application, all treatments showed similar control (82%-99%), except Sharpen + 2,4-D, Deadbolt and Brox-M, which showed lower effect ranging from 79% to 51%. On the final evaluation date, for the 2WAT application, the control increased for all treatments, with Sharpen + 2,4-D, Brox-M, and Starane NXT showing the lowest control ranging from 87% to 86%. All treatments, except for the mentioned three, showed controls higher than 90%. Sharpen showed the need for an MSO adjuvant, the control with Sharpen + MSO was always higher that with the tank-mix Sharpen + 2,4-D, as it can be observed in the Pendleton trial as well.

Impacts: We have observed higher herbicide control 2 WAH than 2DAH, indicating that growers have some time after harvest to control Russian thistle adequately, in fact they should not stop harvesting to control this weed. The use of best herbicide + adjuvant combination is herbicide- adjuvant specific. Saflufenacil plus an MSO adjuvant and bromoxynil products have shown to be good alternatives to control Russian thistle in fallow or post-harvest to glyphosate. Glyphosate effect was improved with the adjuvant Hel-Fire®.

Table 3. Weed control (%) at six weeks after treatment (WAT) of Russian thistle for the different treatments at 2 days after harvest (DAH) and 2 weeks after harvest (WAH) in Pendleton, OR and in Moro, OR in 2019. SEE ATTACHMENT FOR TALBE 3.

Accomplishments

Publications

Research Publications: Adhikari, S., I. C. Burke, and S. D. Eigenbrode. 2020. Mayweed chamomile (Anthemis cotula L.) biology and management – a review of an emerging global invader. Weed Research 60:313- 322. Burke, T. L., and I. C. Burke. 2020. Vernalization affects absorption and translocation of clopyralid and aminopyralid in rush skeletonweed (Chondrillaq juncea). Weed Sci. 68:445-450. Fischer, J.W., M.E. Thorne, and D.J. Lyon. 2020. Weed-sensing technology modifies fallow control of rush skeletonweed (Chondrilla juncea). Weed Technol. 34:857-862. doi.org/10.1017/wet.2020.76. Kumar V, Liu R, Manuchehri MR, Westra EP, Gaines TA, Shelton CW (2021) Feral rye control in quizalofop-resistant wheat in central Great Plains. Agron J. DOI: 10.1002/agj2.20484 Manuchehri, M. R., E. P. Fuerst, S. O. Guy, B. Shafii, D. L. Pittmann, and I. C. Burke. 2020. Growth and development of spring crops in competition with oat in the dryland Mediterranean climate of eastern Washington. Weed Science 68: 646-653. Raiyemo, D. A., W. J. Price, T. A. Rauch, J.M. Campbell, F. Xiao, R. Ma and T. S. Prather. 2020. A Safener Does Influence Pacific Northwest Winter Wheat Varietal Response to Very-Long-Chain Fatty Acid-Inhibiting Herbicides. Western Society of Weed Science Proceedings 73:323. Raiyemo, D., Price, W., Rauch, T., Campbell, J., Xiao, F., Ma, R., Gross, R. Prather, T. (2020). Herbicide safener increases weed-management tools for control of annual grasses in wheat. Weed Technology, 1-10. doi:10.1017/wet.2020.113 Rauch, T. and J. Campbell. 2020. Herbicide Resistant Italian Ryegrass (Lolium perenne spp. multiflorum) Survey in Northern Idaho and Eastern Washington. Western Society of Weed Science Proceedings 73:48. Extension Publications: Lyon, D.J., J. Barroso, J.M. Campbell, D. Finkelnburg, and I.C. Burke. 2020. Best management practices for managing herbicide resistance. (PNW754). Lyon, D.J., A.G. Hulting, J. Barroso, and J.M. Campbell. 2020. Integrated management of downy brome in winter wheat. (PNW668 revision). Lyon, D. J., A. G. Hulting, J. Barroso, and J.M. Campbell. 2020. Integrated management of feral rye in winter wheat (PNW660 revision). Kumar V, Liu R, Lambert T (2020) Response of Kansas feral rye populations to Aggressor herbicide and management in CoAXium wheat production system Kansas Agricultural Experiment Station Research Reports: Vol. 6: Iss. 5. https://doi.org/10.4148/2378-5977.7939

Impact Statements

We have observed higher herbicide control 2 WAH than 2DAH, indicating that growers have some time after harvest to control Russian thistle adequately, in fact they should not stop harvesting to control this weed. The use of best herbicide + adjuvant combination is herbicide- adjuvant specific. Saflufenacil plus an MSO adjuvant and bromoxynil products have shown to be good alternatives to control Russian thistle in fallow or post-harvest to glyphosate. Glyphosate effect was improved with the adjuvant Hel-Fire®.

Date of Annual Report: 05/10/2022

Report Information

Annual Meeting Dates: 03/07/2022 - 03/07/2022
Period the Report Covers: 10/01/2020 - 09/30/3021

Participants

Lovreet Shergill Montana State University lovreet.shergill@montana.edu;
Clint Beiermann Montana State University clint.beiermann@montana.edu;
Ian Burke Washington State University icburke@wsu.edu;
Drew Lyon Washington State University drew.lyon@wsu.edu;
Joan Campbell University of Idaho jcampbel@uidaho.edu;
Traci Rauch University of Idaho trauch@uidaho.edu;
Vipan Kumar Kansas State University vkumar@ksu.edu;
Eric Westra Colorado State University epwestra@rams.colostate.edu;
Caio Brunharo Pennsylvania State University brunharo@psu.edu;
Andrew Kniss University of Wyoming AKniss@uwyo.edu;
Albert Adjesiwor University of Idaho aadjesiwor@uidaho.edu;
Carol Mallory-Smith Oregon State University carol.mallory-smith@oregonstate.edu

Brief Summary of Minutes

We met at Hyatt Regency, Newport Beach, CA on March 6 from 3 to 5 pm before the 2022 Western Society of Weed Science annual meeting. The discussions in the meeting were focused on past and future research projects relevant to the region. The potential to develop multi-state projects for research was also discussed.

Some of the specific topics covered were:

Weed management using CoAXium wheat production system

Seeding direction and weed management

Harvest weed seed control (HWSC)

Integrating cover crops and HWSC in western cropping systems

Developing methods for weed science research

Importance of doing dose-response studies

Feral rye germination and genetic diversity studies to study climate change

Importance of using reverse osmosis water for herbicide efficacy

1. Selection of New Secretary/Chair-Elect

Albert Adjesiwor was nominated by Andrew Kniss and was unanimously elected as the new secretary/chair-elect for next year. Consequently, Lovreet Shergill will organize and conduct the 2023 meeting and Albert Adjesiwor will take notes and file the annual report.

Accomplishments

<h4>1          State Reports</h4> <h4>1.1         Montana – Lovreet S. Shergill</h4> Research Harvest weed seed control (HWSC) for weed management in wheat Grain harvest presents an opportunity for non-chemical weed control. Concurrent maturation of crops and infesting weeds means that crop harvest can result in “harvesting” and subsequent redistribution of problematic weed seeds across the field. The retention of high proportions (> 70%) of total seed production at a height that ensures collection during crop harvest has been recorded for several weed in multiple crops including wheat. In this study, we test the least expensive and most easily implemented HWSC method, known as chaff lining, to determine its efficacy on downy brome in winter wheat using dryland crop rotation systems. We also determined seed retention of problematic weeds in winter and spring wheat cropping systems. Objective 1. Determine chaff lining efficacy on downy brome: The experiment simulating wheat-fallow rotation designed as a factorial, strip-split-block design with 4 reps was initiated in fall 2020. Factors correspond to chaff levels i.e., no-chaff, low, and high (based on average low and high yield data across Montana), and management include untreated, fallow weed control (glyphosate application in summer), and planting (wheat planting at end of summer fallow). Chaff mixed with 500 downy brome seeds/m2 was placed by hand between the crop stubble rows in 12 to 15-inch line width. Weed seed viability was evaluated by including 200 seeds/species in a mesh bag and placed between the soil surface and chaff monticule.             No downy brome emergence was observed in fall 2020 and spring 2021. However, greatest downy brome emergence was observed in no chaff treatment irrespective of the management level. Lowest number of downy brome emerged at both timings in the low and high chaff treatments indicating the weed suppression ability of chaff presence. However, high chaff levels were more effective in suppressing downy brome compared to low and no chaff levels. The viability testing of the seeds recovered at the end of the experiment shows that high chaff level was effective in reducing the seed viability compared to low or no chaff levels. It was also observed that seeds were more deteriorated in high chaff treatments as compared to other treatments at the end of the experiment. Objective 2. Determine weed seed retention at harvest: The field trials were established in randomized design at Southern Agricultural Research Center, Huntley, Montana. Dryland conditions were selected for both trials. In both trials, a minimum of 10 plants of each species were randomly selected to study seed shattering phenology. In spring wheat, only wild oats, and in winter wheat, only feral rye and downy brome were able to survive due to the dry season. The seeds of all three weed species were broadcasted uniformly across the trial before planting wheat. Wheat was planted at 8 inches (row spacing) and 2 inches depth with a commercial seeder. Seed traps were installed around the weed plants a week before wheat physiological maturity to capture shattered seeds. The shattered seeds were collected from traps at weekly intervals up to 28 days after wheat physiological maturity. Finally, we estimated per capita daily seed shattering rate and per capita daily cumulative seed shattering percentage up 28 days after wheat physiological maturity. These metrics are an indicator of how soon farmers should harvest the wheat after physiological maturity to be able to perform harvest weed seed control.             In spring and winter wheat, seed shattering percentage increased over time. The seed shattering percentage of wild oats in spring wheat was <5% at physiological maturity, which was increased to 30%, 50%, 55%, and 60% at 7, 14, 21, and 28 days after physiological maturity, respectively. The lower seed shattering percentage at wheat physiological maturity makes wild oats a suitable candidate for harvest weed seed control in spring wheat. However, a timely harvest is necessary to capture maximum seeds due to the tendency of wild oats to shatter seeds rapidly over time. In winter wheat, seed shattering percentages ranged from 2 to 35% and 4 to 65% for feral rye and downy brome, respectively, over the tested period. Feral rye shattered 2% of seeds at wheat physiological maturity, which was reached at 17%, 30%, 35%, and 35% at 7, 14, 21, and 28 days, respectively, after physiological maturity. Seed shattering of downy brome was recorded around 4% at wheat physiological maturity, which gradually increased and reached 30%, 60%, 65%, and 65% at 7, 14, 21, and 28 days, respectively, after physiological maturity. Both weed species are suitable candidates for harvest weed seed control in winter wheat, considering their low seed shattering percentage at wheat physiological maturity. However, farmers need to harvest the wheat as early as possible after physiological maturity to capture maximum downy brome seeds due to its rapid seed shattering. Impact: This is initial study to explore possibility of using HWSC to manage weeds in Montana cropping systems. The results were shared with growers and researchers through various in-person and virtual presentations and Agricultural Experiment Station Annual Research Report. This research was also demonstrated at 2021 MSU-SARC field day, which was attended by at least 90 people. Herbicide strategies for grass and broadleaf weed control in spring wheat: Montana small grain producers are facing an ever-increasing challenge of managing herbicide-resistant weed species. Current weed control practices in spring wheat production rely on post-emergence (POST) herbicides to control annual weed species. The control of grass weed species in spring wheat is further complicated by having limited available herbicide options, from two mode-of-action (MOA) groups. Grass weed species resistance to group 1 or group 2 mode-of-action herbicides leaves wheat growers with highly limited herbicide options. Across several agricultural systems weeds have rapidly evolved resistance to POST than pre-emergence (PRE) herbicides. Therefore, there is a need to proactively develop weed management strategies that utilize PRE soil residual herbicides along with effective POST applied foliar herbicides.             Our trials at two different locations (Huntley and Kalispell) showed that two-pass herbicide strategies (PRE followed by POST) provided better control over kochia and wild oats compared to onepass (only PRE or POST). Two two-pass herbicide strategies, such as glyphostate + saflufencil fb pinoxaden and pendimethalin fb pinoxaden proved to be the foremost in controlling kochia and wild oats at both research sites. In Huntley, two-pass strategies, such as glyphosate + pyroxasulfone fb pinoxaden and pyroxasulfone + carfentrazone-ethyl fb pinoxaden provided >95% and 100% control over kochia and wild oats, respectively. In Kalispell, two-pass strategies, such as glyphosate + pyroxasulfone fb pinoxaden and pyroxasulfone + carfentrazone-ethyl fb pinoxaden, displayed 100% control over kochia and wild oats; however, some other weed species, such as lambsquaters and pennycress, survived and produced trivial biomass. Regardless of its onepass nature, pyrasulfotole + bromoxynil octanoate + bromoxynil heptanoate + pinoxaden, provided 100% control at both research sites. No crop phytotoxicity was observed at both research sites; therefore, herbicide strategies did not influence grain yield despite enough weed pressure. This might be because of the dry season. Impact: These research findings were shared with Montana wheat growers and research community through various in-person and virtual presentations and Agricultural Experiment Station Annual Research Report. This research was also demonstrated at 2021 MSU-SARC field day, which was attended by at least 90 people. The research aided in providing additional options for growers to manage broadleaf and grass weed control. <h4>1.2         Washington – Drew J. Lyon and Ian C. Burke</h4> Research Italian ryegrass seed shatter in spring wheat: Italian ryegrass (Lolium multiflorum) is a serious weedy threat to crop production in parts of the Pacific Northwest. In addition to high competitiveness with crops, it is now resistant to most herbicides that were once effective for its control. Another mechanism that has contributed to its persistence is the tendency for seeds to disarticulate (shatter) soon after seed maturity and well before crop harvest. This presents a problem as only seeds left on the plant potentially could be captured in the combine grain tank, or better yet, managed with a harvest weed seed control system. We began monitoring Italian ryegrass seed shatter rates on the Palouse in 2017 in winter wheat. Seed shatter in winter wheat averaged about 60% at harvest. We wanted to see if seed shatter rates are different in spring wheat. In 2020, two locations near Pullman, WA were selected. At each location, sampling began when it was evident that most of the florets had finished anthesis (flowering and seed set) and were filling seeds. Ten Italian ryegrass plants were randomly collected from a northeast facing slope, a draw bottom, and a southwest facing slope. Sampling occurred weekly until the wheat crop was ripe, and harvest had begun. From each plant, the number of tillers and spikelets per tiller were counted. In the first two weeks, a representative intact spikelet on each plant was removed from the stem and all florets counted to get an estimate of the potential number of seeds per spikelet if all florets filled; however, it was uncommon for all florets to fill. From all our collections, the total number of florets per spikelet consistently averaged around 12. Maximum floret fill occurred by July 27, but no statistical difference occurred between positions. By August 5, shatter was greatest on the southwest facing position and averaged 3.9 seeds per spikelet, which was a 49% shatter rate for that position. On August 12, seed shatter had significantly increased at all three positions with the southwest position having greater shatter than the northeast. By August 18, there was no statistical change in number of seeds per spikelet for each position, but the southwest position still had greater shatter (fewer seeds per spikelet) than the northwest position. By August 18, or harvest, the southwest position had a shatter rate of 75%, while the draw bottom and the northwest positions had shatter rates of 69 and 61%, respectively. If Italian ryegrass seed management is to be successful, strategies will be needed to collect or destroy the seed before a majority of the seed has shattered. Impact Statement: Grower and industry awareness of herbicide resistance continued to increase in 2021 through a variety of presentations and articles in the popular press and through Timely Topic posts, the Weeders of the West Blog, and WSU Wheat Beat Podcast episodes on the Wheat and Small Grains Website (<a href="http://smallgrains.wsu.edu/">smallgrains.wsu.edu</a>). Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat. <h4>1.3         Idaho - Joan Campbell and Traci Rauch</h4> Research Objective 1. Results. A winter wheat/Italian ryegrass control study evaluated Zidua and Anthem Flex at the highest labeled rates with the following application times:  pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat. Italian ryegrass population was very light and not uniform. Winter wheat yield was similar for all treatments including the untreated check. In another trial, fall or split applications of Zidua controlled Italian ryegrass 90% or better. Fall Zidua followed by spring Axiom controlled Italian ryegrass 93% compared to 82% with Axiom followed by spring Zidua. Outcomes/Impacts: Zidua (group 15) was registered for annual grass control, including Italian ryegrass and rattail fescue, in winter and spring wheat in spring 2014. Zidua registration has aided in control of group 1 and 2 resistant Italian ryegrass. Very few herbicides control rattail fescue. Zidua and Anthem treatments controlled rattail fescue 89-97% in 2018. Winter wheat yield was not reduced by Zidua when 0.5 inch of sprinkler irrigation was applied immediately after planting a spraying on the same day (worst-case scenario). Wheat had minimal injury in 11 conventional-tilled (chisel plowed/field cultivated) sites and in seven direct-seed locations. U of I studies were instrumental in implementing Zidua label changes including an increased use rate and a preplant application time in winter wheat and rotational crops. These label changes have aided growers by giving them more options to improve weed efficacy. Anthem Flex also was registered in wheat fall 2014. Our Anthem Flex studies were useful to FMC when drafting initial rates and timings for their label and subsequent changes. This information will help growers use these products safely and effectively to control grass weeds with minimal crop injury. These registrations provide needed tools to help control herbicide resistant weeds, especially Italian ryegrass. Objective 2. Results: Castle CL, Magic CL, and Sparrow winter wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms October 2020. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. Outlook and Dual Magnum herbicides applied at a 3X rate postplant preemergence caused substantial injury and yield reduction to Sparrow and Magic CL winter wheat varieties at both locations, however injury was more severe at Moscow. Magic and Sparrow yield was increased with safener for Outlook and Dual Magnum at Genesee. At Moscow, Magic and Sparrow yield was increased with safener only for Dual Magnum. Castle CL showed a level of inherent tolerance. Castle yield at Genesee was actually higher in plots treated with Dual Magnum averaged over all safener treatments. Zidua applied at a 3X rate did not cause visual injury or yield effect to any variety at either location. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms spring 2021. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. No spring wheat variety was visibly injured by Outlook, Dual Magnum or Zidua at a 2X rate applied postplant preemergence at two locations. At Genesee, Ryan yield was lower than the nontreated with no safener and higher than the nontreated with safener for Dual Magnum only. Other variety-treatments combinations did not show any yield differences. No effect from safener was observed at Moscow. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass, windgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide mode of action to aid herbicide resistant weed management in wheat. Objective 3. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 106 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used to control Italian ryegrass. Untreated plants are included from each sample. Due to limited greenhouse space, 58 sample screenings are still in progress for Zidua, Dual Magnum, Outlook, Axiom, and Amber. Currently, no sample is resistant to Zidua or Outlook. Amber resistance is widespread at 86%. Axiom and Dual Magnum resistance is 25 and 14%, respectively. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop and herbicide rotation, have altered the makeup of the population. Objective 4. Results: Tillage intensity and duration effects on rattail fescue is ongoing. Severe flooding killed winter wheat in 2019 and downy brome took over. The area is being reestablished to rattail fescue to continue the research.  Success of harvest weed seed control requires weed seed to enter the combine. All other seed will be available to grow the following season. Rattail fescue seed measured at 18 and 7.5 inch header cutting height was 5988 and 3447 seeds per sq foot, respectively. This only included seed still on the plant residue. More seed had shattered and was on the ground. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control in direct seed. Tillage is important but research on how invasive and how often is unknown. Harvest weed seed control data can aid in reducing rattail fescue and other herbicide resistant weed populations. Harvest weed seed control may not provide substantial control for weeds that shatter seed, lodge, or grow low to the ground. This data will help growers take an integrated weed management approach to reducing rattail fescue and increasing crop yield. Objective 5. Results: A group 14 numbered compound was examined as a burndown herbicide in wheat. A burndown application of the compound prior to planting spring wheat was confounded by volunteer winter wheat so Italian ryegrass control and crop response were not evaluated. In a fall burndown application, cotyledon to 2 leaf prickly lettuce was controlled 91 to 99% with this compound plus glyphosate compared to 87% with glyphosate alone. Winter wheat vigor and yield are being evaluated. This compound with be evaluated additionally in 2022. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide resistant weeds. The BASF numbered compound is registered in Australia and may an option for possible control of herbicide resistant broadleaf and grass weeds, especially Italian ryegrass. Objective 6. Results: Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. One blackgrass sample was screened to six herbicides. It was resistant to Beyond, Osprey Xtra, PowerFlex (group 2) and susceptible to glyphosate, clethodim and Axial XL. Three wild oat seed samples were screened with 8 herbicides. Samples were susceptible to clethodim, glyphosate and Axial XL Two samples were resistant to Osprey Xtra, PowerFlex, Everest, and Tacoma (fenoxaprop). One sample was resistant to Beyond. Eight downy brome seed samples were screened to 9 herbicides. All samples were susceptible to Zidua and metribuzin. Four samples were resistant to Osprey Xtra, PowerFlex, Outrider, Olympus and Beyond. Two samples were resistant to glyphosate. These were from a dryland continuous winter wheat rotation. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices. Objective 7. Results: Project personnel participated virtually in cereal schools in north Idaho in January. Due to COVID 19, other presentation opportunities were limited. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems. <h4>1.4         Oklahoma – Misha Manuchehri</h4> Research: Tillage System Impact on Efficacy of Delayed Preemergence Herbicides in Winter Wheat Delayed PRE herbicides can provide season-long Italian ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) control in Oklahoma winter wheat when applied at proper rates and incorporated successfully. Many producers use conventional tillage to prepare fields prior to planting but adoption of conservation and no-till acres is evident. However, crop residue in reduced tillage systems may reduce efficacy of delayed PRE herbicides. To evaluate how previous crop residue might impact DPRE herbicides in Oklahoma winter wheat, a trial was conducted at Perkins, OK during the 2019-20, 2020-21, and 2021-22 growing seasons. Herbicide treatments included metribuzin, pinoxaden, pyroxasulfone, and/or pyroxasulfone + carfentrazone-ethyl applied alone or in tank-mixture in no-till, conservation, and conventional tillage systems. Conservation tillage included a pass of a sweep plow set approximately 10 cm below the soil surface with subsequent rotary hoe action. Conventional tillage systems were disked twice with a tandem disk with a field cultivator following. Crop injury was observed in 2019-20 following pyroxasulfone + metribuzin. In 2019-20, visual ryegrass control prior to harvest was 97 to 99% following pinoxaden POST, pyroxasulfone alone or + carfentrazone-ethyl, pinoxaden, or metribuzin. In 2020-21, pinoxaden applied POST resulted in 100% visual control of ryegrass and 94% less biomass compared to the nontreated. Nontreated and pinoxaden applied DPRE had 98% more ryegrass biomass than any other treatment. In 2019-20, pyroxasulfone + metribuzin resulted in the highest yield, 9% and 22% more compared to pinoxaden DPRE and POST, and the nontreated, respectively. Tillage system affected wheat yield in 2019-20 and 2020-21. Yield decreased ~19% following conventional tillage in 2019 and decreased by ~29% following no-till in 2020 compared to other systems. Soil surface residue influenced by tillage did not affect the efficacy of DPRE herbicides in winter wheat but did affect overall grain yield. Cheat Management in Winter Wheat Cheat (Bromus secalinus) is a difficult-to-control winter annual Bromus species of the southern Great Plains. In past years, cheat has been documented to infest approximately 1.4 million hectares of harvested Oklahoma winter wheat. Biotypes cross-resistant to acetolactate synthase inhibiting herbicides have left growers with minimal management options in conventional and herbicide tolerant systems. Field trials conducted at Lahoma, Oklahoma in 2019-20 and 2020-21 evaluated integrated cheat management using a combination of three management strategies: planting date (optimal, mid-, and late), cultivar selection (one high- and one low-competitive cultivar), and two common herbicides (sulfosulfuron at 35.2 g ai ha-1 and pyroxsulam at 18.4 g ai ha-1). In 2019-20, eight to nine weeks after treatment, visual control increased 11% at mid-planting compared to the optimal and increased 14% at late planting compared to the mid-planting. In 2020-21, similar visual control (~99%) was recorded for mid- and late plantings with 23% greater control than the optimal timing. Cheat biomass during the 2019-20 growing season had no response to planting date, cultivar, or herbicide treatment. During 2020-21, biomass was low (≤ 0.2 g m-2) and 98% less following an application of pyroxsulam or sulfosulfuron compared to nontreated controls. Winter wheat grain at the optimal planting was greatest compared to mid- and late plantings for both growing seasons. In 2019-20, a delay in planting from the optimal to mid- or late timings decreased grain yield up to 21%. In 2020-21, a planting date by herbicide interaction occurred. Delaying planting reduced grain yield, but an application of pyroxsulam or sulfosulfuron increased yield at the optimal planting, resulting in the greatest yields (~6,057 kg ha-1). Pyroxsulam or sulfosulfuron provided a reduction in cheat biomass in 2020-21 but a delay in planting by two to six weeks after the optimal sowing window decreased overall grain yield. CoAXium Wheat Varietal Tolerance to Quizalofop-P-ethyl CoAXium Wheat Production Systems offers postemergence control of many annual grass weeds. However, in the state of Oklahoma, crop tolerance concerns have been raised by agricultural stakeholders. To evaluate the response of winter wheat varieties that contain the AXigen trait (tolerance to quizalofop-P-ethyl), a study was conducted at Perkins and Tipton, Oklahoma and Hays, Kansas during the 2020-21 and 2021-22 growing seasons. Varieties included AP18, Crescent, Fusion, Helix, and Photon. Two herbicide treatments, 1X rate (92 g a.i. ha-1 of quizalofop-P-ethyl plus MSO at 1% vol/vol) and 2X rate (185 g a.i. ha-1 of quizalofop-P-ethyl plus MSO at 2% vol/vol) were applied at three timings: fall (three to five-leaf wheat), early spring (first hollow stem), and late spring (second node detectable). The 2X rate was only applied in the 2021-22 season. For the 2020-2021 growing season at peak visual injury, AP18 exhibited the highest level of damage of 17%, 22%, and 51% at Hays, Perkins, and Tipton, respectively. A similar trend followed for the fall application of the 2021-2022 growing season, with AP18 exhibiting the highest damage (72%) at Perkins across both rates. At Hays, a variety by herbicide rate effect was observed when evaluating percent visual injury. The 2X rate applied to Crescent and Photon resulted in ~80% injury while varieties Fusion and Helix were only injured ~41%. At Tipton, a herbicide rate effect was observed where across all varieties, the 2X rate resulted in an average of 16% more injury than the 1X rate. When evaluating grain yield for the 2020-2021 growing season, a herbicide application timing effect was present at all locations. At Perkins, the early spring timing reduced yield up to 9% compared to the fall, late spring, and nontreated control. A similar trend was observed at Tipton where there was a 9% reduction in yield for the early spring timing compared to the fall. Lastly, at Hays, the late spring application reduced yield 16%, 7%, and 11% compared to nontreated, fall, and early spring, respectively. Impacts: Group 15 herbicides are currently the only chemical tool to manage Italian ryegrass in Oklahoma winter wheat. When using a carrier volume of at least 15 gallons per acre, tillage system likely will not impact ryegrass control. Pyroxsulam and sulfosulfuron are effective tools to manage ALS susceptible cheat. For ALS cross resistant biotypes, CoAXium wheat offers a short-term strategy while crop rotation offers a long-term strategy. Early and late spring applications of quizalofop in CoAXium wheat can result in yield loss. Future research is currently being conducted regarding how CoAXium variety and environmental conditions impact crop response.

Publications

Adhikari, S., Revolinski, S. R., Eigenbrode, S. D., & Burke, I. C. (2021). Genetic diversity and population structure of a global invader Mayweed chamomile (Anthemis cotula): management implications. AoB Plants, 13. https://doi.org/10.1093/aobpla/plab049 Adhikari, S., Burke, I. C., Piaskowski, J., & Eigenbrode, S. D. (2021). Phenotypic trait variation in populations of a global invader Mayweed chamomile (Anthemis cotula): implications for weed management. Frontiers in Agronomy 3:29. <a href="https://doi.org/10.3389/fagro.2021.662375">https://doi.org/10.3389/fagro.2021.662375</a> Adhikari, S., Burke, I. C., Revolinski, S. R., Piaskowski, J., & Eigenbrode, S. D. (2021). Within-population trait variation in a globally invasive plant species Mayweed chamomile (Anthemis cotula): implications for future invasion and management. Frontiers in Agronomy, 3. <a href="https://doi.org/10.3389/fagro.2021.640208">https://doi.org/10.3389/fagro.2021.640208</a>. Dentzman, K., & Burke, I. C. (2021). Herbicide Resistance, Tillage, and Community Management in the Pacific Northwest. Sustainability, 13(4), 1937. <a href="https://doi.org/10.3390/su13041937">https://doi.org/10.3390/su13041937</a>. Flessner, M., Burke, I. C., Dille, J., Everman, W., VanGessel, M., Tidemann, B., Manuchehri, M., Soltani, N, and Sikkema, P. (2021). Potential wheat yield loss due to weeds in the United States and Canada. Weed Technol, 1-8. doi:10.1017/wet.2021.78. Lyon, D.J., J. Barroso, M.E. Thorne, J. Gourlie, and L.K. Lutcher. 2021. Russian thistle (Salsola tragus L.) control with soil-active herbicides in no-till fallow. Weed Technol. 35:547-553. Rodriguez, J., Hauvermale, A., Carter, A., Zuger, R., & Burke, I. C. (2021). An ALA122THR substitution in the AHAS/ALS gene confers imazamox‐resistance in Aegilops cylindrica. Pest Manag Sci. 77:4583-4592. https://doi.org/10.1002/ps.6498. San Martin, C., M.E. Thorne, J.A. Gourlie, D.J. Lyon, and J. Barroso. 2021. Seed retention of grass weeds at wheat harvest in the Pacific Northwest. Weed Sci. 69:238-246. Raiyemo, D. A., J. M. Campbell, R. Ma, W. J. Price, T. A. Rauch, and T. S. Prather. 2021. Herbicide Safener Increases Weed-Management Tools for Control of Annual Grasses in Wheat. Weed Technology 35 (2) p.309.

Impact Statements

Early and late spring applications of quizalofop in CoAXium wheat can result in yield loss. Future research is currently being conducted regarding how CoAXium variety and environmental conditions impact crop response.

Date of Annual Report: 08/24/2023

Report Information

Annual Meeting Dates: 02/27/2023 - 02/27/2023
Period the Report Covers: 10/01/2021 - 09/30/2022

Participants

Joan Campbell, University of Idaho, jcampbel@uidaho.edu;
Traci Rauch, University of Idaho, trauch@uidaho.edu;
Lovreet Shergill, Montana State University, lovreet.shergill@montana.edu;
Clint Beiermann, Montana State University, clint.beiermann@montana.edu;
Ian Burke, Washington State University, icburke@wsu.edu;
Drew Lyon, Washington State University, drew.lyon@wsu.edu;
Eric Westra, Colorado State University, epwestra@rams.colostate.edu

Brief Summary of Minutes

We had a meeting in Room 110D, Boise Centre West, Boise, ID on February 27 from 3 to 5 pm before the 2023 Western Society of Weed Science annual meeting. The discussions in the meeting were focused on these themes:

The Pacific Northwest Herbicide Resistance Initiative (PNW HRI).

The PNW HRI is a collaboration between USDA-ARS and 3 Land Grant Universities (University of Idaho, Oregon State University, and Washington State University)

The overall goals of the PNW HRI were discussed as well as opportunities for collaborative research around the initiative goals. Broadly, the initiative is focused on crop rotations and weed biology and ecology for managing herbicide resistance in the PNW.

Precision Ag and Remote Sensing in Weed Science

There were discussions on emerging technologies and practices for weed management that present collaborative opportunities for weed scientists in the region. Specific technologies or practices included:

Weed IT sprayer, and how to better control grassy weeds

Variable rate technology, weed mapping,

Open-source libraries, firms selling services for mapping weeds.

Target late season escapes – weed seed production.

Weed ID between resistant and susceptible

Harvest Weed Seed Control (HWSC) research in the West

There were discussions on the opportunities and challenges with HWSC in the West. Specific issues or topics discussed included:

PNW adoption – saving 1 glyphosate application.

Farmer collaboration

Issues with farmer adoption, chaff deck (Colorado), slow down of harvest in Idaho in wet years, hail (need to harvest asap), slopes in PNW

Organic farmers may benefit.

Need to estimate how much seed retention is needed for HWSC to be effective.

Low seed retention on weed species

Spring wheat tend to retain more seeds

Remote sensing for collecting data – species level or broad groups

Growers in PNW more interested in impact mills than chaff lining

Funding – WIPM, WSARE,

Wheat fallow rotation, maybe farmers could save one herbicide application.

There was a suggestion to create a sub-committee to work on HWSC.

Other research focus in the region

Cover crops for weed suppression.

Russian thistle dispersion –fences – community management

The potential to develop multi-state projects for research was also discussed.

Eric Westra was unanimously elected as the new secretary/chair-elect for next year. Consequently, Albert Adjesiwor will organize and conduct the 2024 meeting in Denver and Eric Westra will take notes and file the annual report.

1 State Reports

1.1 Idaho – Albert Adjesiwor, Joan Campbell, and Traci Rauch

Research

Objective 1. Results: Castle CL, Magic CL, and Sparrow winter wheat varieties with and without the safener ConcepIII were seeded at the U of I Moscow and Genesee farms in October 2021. Outlook and Dual Magnum were applied after seeding along with an untreated control. Outlook and Dual Magnum herbicides applied at a 2X rate post-plant preemergence caused substantial injury and yield reduction to all winter wheat varieties at both locations, however, injury was more severe at Moscow. Yield of all varieties was increased with safener at both locations. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without the safener were seeded at the U of I Genesee farm in spring 2022. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. Yield of all varieties and for all herbicides was increased with safener. Yield averaged over all herbicides and varieties was 70 and 51 bu/a with and without safener, respectively.

Objective 1. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass, windgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide mode of action to aid herbicide-resistant weed management in wheat.

Objective 2. Results: Kerb was applied at 1.25 and 2.5 pt/a in fall and spring before planting spring canola, pea, chickpea and lentil at Moscow and Genesee. There was no injury to any of these crops. Winter wheat was planted in October 2021 to assess crop response. Wheat yield was reduced more with the high rate than the low rate at both locations. The very dry year in 2021 was not conducive to herbicide breakdown and the dry, hard soil in fall 2021 resulted in a very shallow planting depth. This experiment has been repeated and wheat was planted in October. No injury was evident after crop emergence fall 2022. In a second experiment, Kerb was applied prior to spring wheat planted at two depths. The shallow planting had more injury. This experiment is being repeated with winter wheat and no injury was evident fall 2022 at either depth.

Objective 2. Outcomes/Impacts: Kerb is an old herbicide that is active on many grass (Italian ryegrass, downy brome, wild oat, jointed goatgrass, etc) and broadleaf weeds. Canola and pulse crops are tolerant to this herbicide. The following wheat crop must be tolerant to residual amounts of herbicide to obtain a label for these crops. Kerb would be an additional chemistry to help with control of some problematic weeds.

Objective 3. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 103 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used to control Italian ryegrass. Untreated plants are included from each sample. All samples have been screened for Zidua, Dual Magnum, Outlook, Axiom, and Amber. No sample was resistant to Zidua or Outlook. Amber resistance is widespread at 91%. Axiom and Dual Magnum resistance is 20 and 10%, respectively.

Objective 3. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop, and herbicide rotation, have altered the makeup of the population.

Objective 4. Results: The 2 sites were taken over by downy brome. It is difficult to separate information on rattail fescue only. Downy brome was unaffected by any of the tillage treatments. Rattail fescue was reduced by tillage, but not eliminated with these treatments. Data over the length of the experiments will be summarized in the coming months.

Objective 4. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control in direct seed.

Objective 5. Results: A group 14 numbered compound from BASF was examined as a burndown herbicide in wheat. In a fall burndown application, cotyledon to 2 leaf prickly lettuce was controlled 91 to 99% with BASF compound plus glyphosate compared to 87% with glyphosate alone in November. By May, the highest BASF compound rate tended to have the best residual prickly lettuce control at 68%. A group 27 numbered compound from Corteva was examined for broadleaf weed control (Russian thistle) in wheat but was not evaluated due to a nonuniform weed stand. Crop tolerance was excellent. This compound with be evaluated additionally in 2023. Plant health chemicals, fungicides, and nutrients were also evaluated with and without herbicides.

Objective 5. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide-resistant weeds. The BASF compound is registered in Australia and may be a tool for possible control of herbicide-resistant broadleaf and grass weeds, especially Italian ryegrass. The Corteva compound is registered in corn in the USA and may be another option for broadleaf weed control.

Objective 6. Results: Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. One ventenata sample was screened to six herbicides. It was resistant to Beyond and susceptible to PowerFlex, Osprey Xtra, glyphosate, clethodim and Axial XL. One wild oat seed sample was screened with 7 herbicides. It was resistant to Assure II and susceptible to clethodim, glyphosate, Axial XL, Beyond, Osprey Xtra, and PowerFlex. One downy brome seed sample was screened to 6 herbicides. The sample was resistant to Beyond and susceptible to Zidua, metribuzin, Osprey Xtra, PowerFlex, and Aggressor.

Objective 6. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices.

Objective 7. Results: Project personnel participated virtually in cereal schools in north Idaho in January. Research information was presented at the Western Society of Weed Science meeting in March. Cereal research was also presented at field days in June and July.

Objective 7. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems.

Objective 8. Alternatives to glyphosate for pre-plant wheat control in wheat and barley cropping systems. Field experiments were conducted at the University of Idaho Research and Extension Centers in Kimberly Center and Aberdeen, Idaho in 2021 and 2022, to evaluate weed control, crop response, and economics of different herbicide programs. At Kimberly, the soil was a Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids). The soil at Aberdeen was a Declo loam (Coarse-loamy, mixed, superactive, mesic Xeric Haplocalcids).

The wheat and barley studies were established side-by-side at each location. For each crop, there were 18 different herbicide and herbicide combination treatments, including the untreated check. Treatments were arranged in a randomized complete block with four replications. Each plot was approximately 3 m wide by 9 m long. Herbicides were applied using a CO₂-pressurized bicycle sprayer delivering 144 L ha^-1 at 207 kPa with TeeJet 11002DG nozzles on August 25th, 2021, and September 14th, 2022 in Kimberly, and September 2, 2021, and September 15th, 2022 in Aberdeen. At the time of herbicide application, the average weed heights in Kimberly in 2021 and 2022 were common lambsquarters (12, 3 cm), kochia (14, 3 cm), redroot pigweed (12, 3 cm), green foxtail (8, 3 cm). In Aberdeen, common lambsquarters, kochia, redroot pigweed, and green foxtail were about 3 to 6 cm tall in both years.

Each year and for each crop, weed control efficacy (by weed species) was visually assessed at 7 days and 14 days after treatment on a scale of 0 to 100%, with 0% being no weed control and 100% being complete weed control. Within 28 days after herbicide applications, winter wheat (“Brundage”) and winter barley (“Charles”) were planted at a rate of 112 kg ha^-1. In the spring of 2022 and 2023, visible crop injury was assessed on a scale of 0 to 100% with 0% being no crop injury and 100% being total crop destruction. Immediately following crop injury assessments, all plots were sprayed with post-emergence herbicides to control emerging weeds and eliminate or reduce competition from weeds. This was done to ensure that any growth or yield reduction was due to crop response to herbicides and not weed competition. The costs of the weed control programs were calculated using the average unit herbicide cost from local agrochemical dealers.

Objective 8. Results: Majority of the herbicide treatments applied alone or in mixtures provided weed control statistically similar to glyphosate. Glufosinate, paraquat, tiafenacil, and topramezone applied alone as well as the low rate of glyphosate provided less than 90% control of common lambsquarters. However, mixtures containing these herbicides provided very good (>90%) control of common lambsquarters. This demonstrates the importance of herbicide tank-mixtures for effective weed control. There was herbicide by location interaction effect on common lambsquarters control. This was possibly due to differences in weed size and weather conditions at the two locations.

Redroot pigweed control was also significantly influenced by herbicide and the herbicide by year by location interaction. The interaction effect of these factors on redroot pigweed control was due to weed size and weather condition differences across years and experimental sites. Only topramezone applied alone provided less weed control compared to glyphosate. All other herbicides, whether applied alone or in mixtures provided similar weed control as glyphosate. We can infer that almost all these treatments would be good preplant burndown treatments for a field that had a high population of redroot pigweed. Since redroot pigweed grows later in the growing season, having a burndown in the late summer to early fall is ideal, especially if redroot pigweed is a predominant weed in the field.

Nearly all herbicide treatments except for topramezone applied alone provide very good (>90%) control of kochia. Topramezone was the least effective herbicide for kochia control. Only around 50% kochia control was achieved with the topramezone treatment. Mixtures of topramezone with other herbicides provided better kochia control. There was no effect of year, location, or their interactions on kochia control.

One characteristic that makes glyphosate an ideal preplant burndown herbicide is its ability to control both grassy and broadleaf weeds. While there are multiple herbicide options for broadleaf weed control before or after planting small grains, grassy weed control remains very challenging. It was observed that glyphosate remains one of the best options for grassy weed control. Interestingly, green foxtail control was much more effective with topramezone compared to the broadleaf weeds. Nonetheless, the results showed that there are other effective alternatives to glyphosate for pre-plant grassy weed control. For example, glufosinate, paraquat, and their mixtures provided similar green foxtail control as glyphosate.

After herbicide treatments were applied, the wheat and barley were evaluated for crop injury to determine if the herbicide treatments were as safe as glyphosate treatments. No physical signs of herbicide damage were observed, and the growth of both the wheat and barley was observed as normal. Crop yield was evaluated in 2022, and there were no effects of herbicide treatments on wheat or barley yield. Wheat yield was 7,666 kg ha-1 in the untreated check and 6,927 to 8,877 kg ha-1 in the herbicide treatments. Barley yield was 8743 kg ha^-1 in the untreated check and 6,591 to 9,550 kg ha^-1 in the herbicide treatments. Visible injury evaluations in the spring of 2023 also showed that there were no injuries from the pre-plant herbicide applications. Thus, these herbicide alternatives have all been shown to be safe alternatives for pre-plant burndown weed control in these cereal crops.

The cost of the pre-plant herbicide programs was compared to the price of glyphosate due to glyphosate being the standard pre-plant burndown herbicide treatment that growers use for weed control. It is observed that there were at least six other treatments that may be economical alternatives to glyphosate for pre-plant weed control. The cheapest treatment was paraquat at $15.9 ha^-1 and depending on the weed species had between 85 to 99% control. This proves that there are indeed cheaper alternatives to glyphosate that still have high levels of control for all the weed species in this study. While more money might be spent on herbicide mixtures in the short term, there is a long-term benefit as a proactive herbicide resistance management strategy.

Objective 8. Outcomes/Impacts: These research findings were shared with Idaho Wheat and Barley Commissions through in-person meetings and recorded presentations. Results were also published on the Weeders of the West Blog and demonstrated at 2022 Snake River Weed Tour which was attended by nearly 100 stakeholders. The research aided in providing additional herbicide options to growers for pre-plant weed control to reduce reliance on glyphosate.

1.2 Washington – Drew J. Lyon and Ian C. Burke

Research

Evaluation of BAS 85101H for Russian thistle control in chemical fallow. A field study was conducted at the Lind Dryland Research Center near Lind, WA to assess BAS 85101H alone and in tank mix combinations with glyphosate for the control of Russian-thistle in chemical fallow. BAS 85101H is an herbicide in development by BASF Corporation. The soil at this site is a Ritzville silt loam with 1.3% organic matter and a pH of 5.6. The field was previously in winter wheat. The Russian-thistle population was uniform across the trial area but was at a low level of 12 plants per square yard. The plants ranged from 6 to 16 inches in diameter (mean = 9.0 inches) and a height that ranged from 2.5 to 10 inches (mean = 6.0 inches). Treatments were applied on June 30, 2022, with a CO2-powered backpack sprayer set to deliver 10 gpa at 47 psi at 2.3 mph. The applications were made at an air temperature of 86°F and relative humidity of 21%, and winds were out of the south at 8 mph. The station received 1.73 inches of rain in June (average = 0.78 inches), and 0.35 inches in July (average = 0.28 inches) following the herbicide applications. Air temperatures were not significantly different from the normal for this time. RoundUp PowerMax applied at either 16 or 22 fl oz/a did not control Russian thistle (Table). BAS 85101H, Sharpen and Reviton all showed quick-acting burndown on Russian thistle 7 days after treatment (DAT). Fourteen DAT, it was evident that Russian-thistle plants were recovering in the Sharpen- and Reviton-treated plots. This trend continued with these two treatments up to the final rating 27 DAT. BAS 85101H provided nearly complete control of Russian thistle through the final rating 27 DAT. The addition of RoundUp PowerMax at either rate, did not significantly change the level of Russian thistle control provided by BAS 85101H, Sharpen or Reviton as stand-alone treatments. With the above-average precipitation preceding the study, it was thought that the Russian thistle plants were not under significant drought stress and that glyphosate would provide acceptable control. It may have been that the glyphosate rates chosen in the study were too low to provide control. BAS 85101H really stood out in this study. Our hope is that this product will be brought to the market and provide another herbicide other than glyphosate or paraquat that will offer excellent control of Russian-thistle.

Pyroxasulfone for Downy Brome Control in Winter Wheat. The study objective was to evaluate pyroxasulfone with GA3 for downy brome (Bromus tectorum) control in winter wheat. GA3 is a plant growth regulator that stimulates seed germination and alleviates seed dormancy in laboratory and greenhouse conditions. The combination of pyroxasulfone and GA3 has potential to reduce downy brome seedbanks in winter wheat production systems. A study site was established at WSU Wilke Farm near Davenport, WA and downy brome populations were present at the time of study establishment. Preemergence applications of pyroxasulfone, pyroxasulfone with GA3, and pyroxasulfone with GA3 and metribuzin were applied to winter wheat in the fall of 2021 (table 1). Treatments were applied with a CO2-powered backpack sprayer and a 5-foot boom with four Teejet 11002VS nozzles. The sprayer was calibrated to 15 gallons per acre. The study was conducted in a randomized complete block design with four replications and plots were 10 ft wide by 30 ft long. Treatments were assessed by visual estimation of winter wheat density at 224 days after treatment with pyroxasulfone and downy brome density per m2 at 250 and 263 days after treatment with pyroxasulfone. All data were subjected to an analysis of variance using Agricultural Research Manager software system (ARM ver. 2022.7, Gylling Data Management). There was no difference in winter wheat density between treatments at 224 days after treatment with pyroxasulfone as a preemergence herbicide.

At 250 days after treatment, downy brome density per m² was reduced in all treatments (density ranged from 1 to 5 plants/m2) compared to the nontreated plots (15 plants/m²). Yield was similar among treatments and greater than the nontreated. GA3 did not affect downy brome control with pyroxasulfone, but pyroxasulfone was effective for reducing overall downy brome density in winter wheat.

Accomplishments

Grower and industry awareness of herbicide resistance continued to increase in 2022 through a variety of presentations and articles in the popular press and through Timely Topic posts, the Weeders of the West Blog, and WSU Wheat Beat Podcast episodes on the Wheat and Small Grains Website. Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

Publications

Kniss, A.R., Mosqueda, E.G., Lawrence, N.C., Adjesiwor, A.T. 2022. The cost of implementing effective herbicide mixtures for resistance management. Adv Weed Sci 2022; 40(spe1): e0202200119 Lyon, D.J., and M.E. Thorne. 2022. Smooth scouringrush (Equisetum laevigatum) control with glyphosate in Eastern Washington. Weed Technol. 36:457-461. Spring, J.F, S.R. Revolinski, F.L. Young, D.J. Lyon, and I.C. Burke. 2022. Weak population differentiation and high diversity in Salsola tragus in the inland Pacific Northwest, USA. Pest Manag. Sci. 78:4728-4740. Tautges, N. & Borrelli, K. & Goldberger, J. & Machado, S. & Fuerst, E.P. & Roberts, D. & Burke, I. C. (2022). Chapter 3 - Growing small grains organically in the semiarid West: A review of markets and management practices to optimize productivity and sustainability. Advances in Agronomy 171, 111-141. https://doi.org/10.1016/bs.agron.2021.10.005. Revolinski, S.R., Maughan, P.J., Coleman, C.E. and Burke, I.C., 2023. Preadapted to adapt: underpinnings of adaptive plasticity revealed by the downy brome genome. Nature Communications (In Press) Extension Publications and Proceedings: Adjesiwor, A.T., D.J. Lyon, J. Barroso, and J.M. Campbell. 2022. Integrated management of wild oat in the Pacific Northwest. (PNW759). Brunharo C, Barber T, Bond J, Brosnan J, Campbell J, Geddes C, Rana N, Stephenson D, Subramanian N, Bagavathiannan M, Pennsylvania State University; University of Arkansas; Mississippi State University; University of Tennessee; University of Idaho; Agriculture and Agri-Food Canada; Bayer Crop Science; Louisiana State University; Texas A&M University. 2022. Revised Herbicide Mode of Action Classification. Western Society of Weed Science. Page 30. https://wsweedscience.org/wp-content/uploads/WSWS-Proceedings-2022-v2.pdf  Lyon, D, Barroso, J, Burke, I, & Campbell, J. 2022. Managing Herbicide-Resistant Annual Grass Weeds in Dryland Wheat Production Systems of the PNW [Abstract]. ASA, CSSA, SSSA International Annual Meeting, Baltimore, MD. https://scisoc.confex.com/scisoc/2022am/meetingapp.cgi/Paper/141977 Rauch, T.A and J. M. Campbell. 2022. Field Disturbance and Greenhouse Irrigation Effects on Italian Ryegrass Control with Pyroxasulfone. Western Soc. Weed Sci. Proceedings. 75:19.

Impact Statements

Growers were provided with efficacy and crop safety information for newer herbicide products in wheat.