Duration: 10/01/2006 to 09/30/2011

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Weed management is generally viewed as a major challenge in conventional, transitional and organic cropping systems. Control of weeds in agriculture costs the U.S. economy more than $15 billion annually, more than the cost of controlling insects and diseases combined (Bridges 1992). Although organic cropping systems are often highly profitable anyway, weed densities frequently boarder on or exceed tolerable levels (Mohler 2007), and surveys of organic growers and studies of organic farms indicate that weeds are a major production problem (Peacock 1990, OFRF 1999, Bond and Grundy 2001). Moreover, existing methods for controlling weeds on organic farms depend on excessive soil disturbance, resulting in loses in soil quality.

Currently, little research is directed toward the weed management needs of organic producers. New methods like organically certifiable herbicides and weed management with cover crops are needed. There is also a need to evaluate existing approaches like nutrient management for weed control and the mechanisms of cultivator action. Conversations with growers indicate that fear of uncontrolled weeds is frequently a factor inhibiting adoption of organic practices. Development of new weed management methods and improvement of traditional methods will speed adoption of organic practices, thereby reducing use of both herbicides and other pesticides. This will improve environmental quality and reduce expenses for farmers. Better weed management options will also improve yield and profits, thereby strengthening local communities.

All four objectives of the study are direct responses to growers' requests for information at talks and workshops. Interest in natural product herbicides has been growing rapidly, and is reflected in increasing sales of vinegar, clove oil, and citric acid based products. Such products have the potential of reducing organic growers' dependence on soil disturbance for weed management. Unfortunately, reliable information on the optimal use of these products has lagged behind. Organic growers also continue to express strong interest in the use of cover crops to balance goals of weed management and improvement in soil health. For example, at a 2005 needs-assessment workshop led by several organic growers (hosted by Cornell Universities' Organic Production and Marketing Project Work Team), cover crops for weed management were identified as a major research priority. Organic growers have long shown interest in nutrient effects on weed management. In particular, growers are interested in how cation ratios and micronutrient availability affect weed management. Unfortunately, most of the information currently available is anecdotal and contradictory. Organic growers throughout the U.S. are annually spreading thousands of tons of gypsum on circum-neutral soils to increase available calcium and control foxtail, with essentially no research data to support or refute the practice. Either growers are throwing away thousands of dollars per year on unnecessary supplements or other growers are suffering yield losses by not using them. Finally, improved information on cultivation is essential for successful control of weeds on organic farms. Cultivation is the primary means of weed management in organic systems. The whole thrust of objective 4, namely exploration of the different mechanisms whereby mechanical soil disturbance kills weeds and how weeds differ in their susceptibility to different kinds of disturbance, is directly relevant to questions and suggestions organic farmers Klaas and Mary Howell Martens raised in their recent article in The New Farm electronic journal (http://www.newfarm.org/ features/2005/0105/earlyweeds /index1.shtml). Such mechanistic information should facilitate more efficient use of cultivation tools, and help minimize their potentially destructive effect on soil health.

Even more than in conventional agriculture, the problems of organic farmers and approaches to their solution vary greatly in response to local soil and climatic conditions. Thus, a comparative approach that examines similar management methods across the U.S.A. and beyond will help identify common principles, and indicate how they have to be modified to fit local conditions. A multi-state approach is therefore ideal for addressing problems in organic weed management.

The research proposed here is intended to (i) increase the range of weed management options available to growers, (ii) improve overall weed management on a wide range of organic and transitional farms, (iii) encourage the transition to organic practices by reducing fear of unmanageable weed problems, (iv) improve soil health by substituting natural product herbicides and cover crops for tillage and cultivation, and (v) improve the overall profitability of transitional and established organic farms by decreasing labor and yield losses to weeds. The proposed research should also foster collaboration between weed scientists and help them leverage funding from other sources to pursue these topics in more depth. In particular, the proposed project will help leverage renewal of a long-term cropping system study funded by the USDA-Integrated Organic Program by providing some quick results through cultivation experiments nested within that study. The new project should also be helpful in leveraging funding proposals to the NE-IPM program, SARE and PMAP programs integrating buckwheat and mustard cover crops and natural product herbicides into weed management programs.

Related, Current and Previous Work

Work related to Objective 1: Reducing effective rates of natural product herbicides

Natural product herbicides have the potential to play an important role on organic farms by reducing reliance on tillage and cultivation and replacing expensive hand weeding operations. Commercially available natural product herbicides containing either vinegar (acetic acid) or clove oil (eugenol) are increasing in demand by organic growers, but only limited information is available on their effective use. Greenhouse and field trials have shown that vinegar applied in concentrations between 10 and 30% can effectively suppress multiple broadleaf weed species (Chandran, 2003; Johnson et al. 2003; Curran et al. 2003; Radhakrishnan et al. 2002), but cannot consistently control grasses (Curran et al. 2003). Clove oil at concentrations of 1 to 10 % has also been demonstrated to provide good control of several broadleaf weed species in some studies (Curran et al., 2003; Lindsay, 2003; Tworkoski, 2002) but inconsistent control in others (e.g. Ferguson 2004).

Although natural product herbicides are potentially valuable, effective rates of currently available products are often both prohibitively expensive and potentially toxic. For example, 20% vinegar (acetic acid) can cause skin burns and eye damage (Sullivan 2004). Clove oil based herbicides like Matran II, can cost over $250/A if broadcast at even the lowest recommended rate. Preliminary research suggests that effective rates of these products can be reduced through use of better adjuvants and improved knowledge of the impact of weather conditions on efficacy. For example, in preliminary greenhouse trials, clove oil used with a silicon adjuvant was effective in controlling weeds at a 1% concentration (Lanini, unpublished). Anecdotal evidence also suggests that the effectiveness of these products may be increased under sunny conditions or high relative humidity, but more information is needed to assess these factors (Curran, Haar, unpublished). Reductions in rates may also be achieved through better characterization of the sensitivity of specific weeds at different growth stages. Sensitivities of many important weed species remain unknown, and interpretation of studies involving other species is often difficult given ambiguities in the volume of product applied and the growth stage of target weeds.

A search of the USDA Research database found studies focusing on identification of new natural product herbicides and modes of action (Projects 6408-21410-00D); use of vinegar at high rates (as a soil drench) to control Spartina alterniflora (Projects 5325-22000-018-04R and 5325-22000-018-08R); and testing of clove oil (Project FLA-HOS-04013) or vinegar (Project WVA00447) at a single location. To our knowledge, no projects are examining the use of vinegar and clove oil across multiple sites to better understand the impact of environmental conditions on efficacy. Nor are any studies focusing on the use of adjuvants to reduce rates.

Work related to Objective 2: Effects of cover crop planting date and method of incorporation on weed suppression

Buckwheat and crucifer cover crops can provide multiple benefits within organic and sustainable production systems including suppression of plant pathogens (Mojtahedi et al. 1993; Smith et al. 2004), improvements in soil health (Sarrantonio 1994), attraction of beneficial insects (Sarrantonio 1994) and suppression of weeds (Gallandt and Haramoto 2004). Cover crops can suppress weeds through direct interference during cover crop growth, or by altering soil physical, chemical, or biological properties following mowing or incorporation (Teasdale 1998). Buckwheat has long been appreciated for its ability to grow so rapidly that weeds get no chance to make headway against it (Stone 1906). Buckwheat can also suppress weeds through the release of allelochemcals like diethyl phthalate (Eom, 2001). For mustards, glucosinolates in decomposing residue are hydrolyzed by myrosinase to produce a number of active weed-suppressive allelochemicals including isothiocyanates (Al-Turki and Dick 2003; Gardiner et al. 1999; Mithen 2000; Morra and Kirkegaard 2002).

Field studies testing the weed suppressive ability of these cover crops have had variable results. For example, rapeseed and white mustard green manures reduced weed biomass in subsequent potato (Boydston and Vaughn 2002) and pea (Al-Khatib et al. 1997) crops, but incorporated canola provided inconsistent weed control in strawberries (Forcella et al. 2003). In part, such variable results may reflect differences in environmental conditions between studies. Such differences can influence weed suppressive ability by changing (i) the relative growth rates of weeds and cover crops (e.g. Brainard and Bellinder 2004) or (ii) the total biomass or concentration of allelochemicals in plant tissue (Kirkegaard et al. 2000; Morra and Kirkegaard 2002; Lazzeri et al. 2004; Oliver et al. 1999; Warton et al. 2001).

The method of incorporating cover crops may have an important effect on both their efficacy in controlling weeds as well as their compatibility with sustainable production systems. In crucifer tissues, incorporation methods may influence the extent of cell wall disruption, which determines the extent of myrosinase release, and hence the extent of glucosinolate hydrolysis to active allelochemicals (Warton et al. 2001; Morra and Kirkegaard 2002). For buckwheat, incorporation methods may be important not only for influencing allelochemical release, but also for insuring that regrowth does not occur and that tissues decompose fast enough to facilitate planting of a subsequent crop with minimal field preparation costs.

A search of the USDA Research Database located several projects involving weed suppression by buckwheat and crucifer cover crops including those evaluating weed suppression in subsequent crops including spinach and lettuce (Project CA-D-PLS-7010-CG), soybean (3625-22610-001-01T) and potato (5354-21660-001-00D). Project OHO00149 established suitable planting dates for crucifer cover crops in Ohio, developed techniques for measuring the level of myrosinase in soil, and evaluated control of several weed species. Our proposed work would build on these studies by testing cover crops across multiple sites, and by evaluating the role of incorporation methods in optimizing weed suppression. By utilizing the same genotype, weed spectra, seeding rates, and incorporation methods across many sites, we intend to develop a clearer understanding of how environmental conditions influence the effectiveness of these cover crops for weed suppression. Our work will also facilitate better understanding of the relationship between cover crop biomass and weed suppression, and help separate the effects of weed suppression during crop growth from weed suppression following cover crop incorporation.

Work related to Objective 3: Effects of soil nutrients on crop-weed competition and weed management.

Popular organic agriculture publications assert that weeds represent particular soil conditions that may be managed through proper manipulation of pH, organic matter, base saturation ratio, and micro-nutrients (Walters 1999). Unfortunately, precise recommendations for managing weeds with soil nutrition are not documented by Walters (1999) or the many soil testing services and crop consultants who market this approach to organic farmers. Some scientific evidence, however, does suggest that soil nutrition affects weed populations.

DiTomaso (1995) reviewed fertility effects on weeds. Many weed species accumulate higher concentrations of macro- and micronutrients than can most crops (Vengris et al 1953, Alkämper 1976), and fertility can affect weed abundance. For example, Taraxacum officianale, increased 17- to 20-fold in response to K fertilization in the classic Park Grass experiment in Rothamsted, UK (Tilman et al. 1999). Andreasen et al. (1991), in Denmark found that certain species were associated with particular organic matter, pH, P, K, Mg, or Mn conditions. Many common weed species, however, were unaffected by variation in soil P, K, or Mn. Increasing fertility level in some cases favors the crop relative to weeds (Tollenar et al. 1994), but more often appears to increase weed growth at the expense of the crop (Liebman and Mohler 2001, Bjorkman, Mohler and DiTommaso, unpublished data).

The percentage of the soil's CEC occupied by various cations is termed the "base saturation ratio". Based on the research of William Albrecht, many organic farmers attempt to balance relative amounts of cations to produce ratios that are thought to promote soil health and crop growth (Schonbeck). Acres U.S.A., a national magazine and organization (www.acresusa.com) popular among organic growers has long advocated this approach to fertility management (Walters and Fenzau 1992). Albrecht proposed an optimum base saturation ratio of 65-75%Ca, 10-15% Mg, 2-5% K, 0.5-3.0% Na and 10-15% H. Low Ca and high Mg or K are thought to "tighten" the soil, reducing aggregation and degrading physical properties. Supposedly, this decreases beneficial soil biota and humus formation, weakens crops, and increases pest insects, diseases and weeds (Schonbeck). The agricultural research community has largely ignored or rejected the base saturation approach to fertility management (e.g., Goldstein 1990; Liebhardt 1981). Schonbeck recently evaluated the base saturation ratio hypothesis at five locations in the southern USA. A high Ca treatment created by annual application of calcitic lime, with or without gypsum, shifted base saturation closer to that recommended by Albrecht. Averaged over the five sites it failed to affect soil physical properties, including bulk density, water infiltration rate, and soil strength, but it did significantly affect these properties at some sites (Schonbeck). Percent weed cover was measured at 2 of the 5 sites and was also not affected. Similarly, Pierce et al. (1999) found Digitaria sanguinalis growth decresed with increasing Ca, and germination decreased with addition of MgCO3. Growers report that improvements in soil quality improve the efficacy of cultivation (Anonymous 1994), but this was not detected in a study comparing cultivation mortality of Chenopodium album in replicated plots that differed considerably in soil organic matter and proportion of water stable aggregates (Gallandt 2004).

A search of the USDA Research Database located several studies examining the effects of soil fertility management practices on weed-crop interactions (e.g. Project NYC-145468; ProjectNH00419). The recently completed project IOW06586 examined the interactive effects of N fertility and light on weed crop competition. No studies were identified examining the effect of base saturation ratios or micronutrients on weed management.

Work related to Objective 4: Causes of weed mortality during cultivation.

Most recent studies of cultivation have focused on integration of cultivation with banded or reduced rates of herbicides. Generally these integrated systems have performed well (Mulder and Doll 1993, Mt. Pleasant et al. l994, Parks et al. 1995, Mulugeta and Stoltenberg 1997, Colquhoun et al. 1999). When modern in-row cultivation systems have been compared to conventional weed management with herbicides, cultivation often performs as well as chemical management in terms of weed control, crop yield and profitability (Schweizer et al. 1994, VanGessel et al. 1995, Mohler et al. 1997).

Only a few implements have been systematically studied for effects of factors like speed, proximity to the row, or number of passes for even a single crop (Rasmussen 1991, Ascard 1994, Melander 1997). Although more such studies are needed, sufficiently testing many implements in a wide range of crops and conditions will be difficult. Acquiring mechanistic information on how cultivators kill weeds and under what conditions of size and soil moisture various species are susceptible to the different types of disturbance provides an alternative approach for producing recommendations on cultivator use. To what extent do various implements kill weeds by fragmentation, burial, or desiccation due to uprooting? Conversely, how does size and growth stage affect susceptibility to various types of disturbance by cultivators? Very few studies have approached these questions. Fogelberg and Dock Gustavsson (1999) showed that a vertical-axis brush weeder killed more weeds by uprooting than by burial, though both mechanisms caused significant mortality. Kurstjens and colleagues studied seedling mortality from tine weeding.. They found that at an operating speed of 1.8 m/s, 60% of 1 cm Lolium perenne seedlings were buried but only 40% of 6 cm seedlings (Kursjens and Perdok 2000). Only about 20% of the stiffer Lepidium sativum seedlings were buried. At slow speeds (1.2 m/s), larger plants of both species were less susceptible to soil covering, but at higher speed (2.4 m/s) larger plants were slightly more susceptible. Half of seedlings that were just emerging were uprooted by a tine weeder whereas only 21% of established seedlings were uprooted (Kurstjens et al. 2000). Increasing working depth from 1 cm to 3 cm doubled the percentage of plants uprooted. Kurstjens et al (2004) used data on anchorage forces of seedlings to model uprooting by a tine weeder, and predict how variation in speed, working depth, and soil moisture affect differential mortality of weeds and crops.

A search of the USDA Research Database located several studies examining various cultivation tools in different crops including strawberries (Project NYC-145424), lettuce (NYC-145582), sweet corn and potato (Project KYX-10-02-35P); use of robot guided precision cultivators (CA-D-PLS-7316-CG); and effects of cultivation timing on efficacy (OHO00216). To our knowledge, no studies are focusing on the mechanisms by which cultivators kill weeds, and their interactions with soil moisture and implement type.

Summary of work by the previous project

Earlier multi-state weed projects demonstrated that the amount of cover crop residue produced during the winter was insufficient to effectively suppress weed seedling emergence. One objective of the last project was to determine whether concentrating crop residue over the row could, in conjunction with between row cultivation, provide good weed control without herbicides. Experiments with corn showed that even concentrating rye residue over the row did not achieve a sufficient residue density to give good in-row weed control. Also, some rye survived mowing and competed with the corn. Experiments with soybean achieved high in-row biomass of rye-hairy vetch residue, but this reduced soybean stand, and weeds that did penetrate the residue then grew vigorously in the gaps. Thus, this seemingly reasonable approach to using crop residue for weed suppression in herbicide free cropping systems appears fraught with difficulties.

Multi-state weed projects in the 1990's showed that low rates of crop residue often promote weed seedling emergence rather than suppressing it. To model the balance between promotion by improved soil moisture and suppression by physical and chemical interference, studies were made of the relation of seed germination to moisture potential. The standard PEG method overestimated germination percentage at the biologically most interesting intermediate moisture potentials relative to soil equilibrated on a pressure plate apparatus. Some weed species showed appreciable germination even at -1,000kPa.

Rye variety trials at six locations identified regionally adapted varieties for use as cover crops. 'Wheeler' rye showed greatest weed suppressive ability in bioassays, but only showed greater weed suppression in the field in a few site-years. Previous multi-state projects showed that subterranean clover was useful as a living and dead mulch, but had limited winter hardiness. Screening of over 400 subterranean clover lines failed to find any that were more cold hardy than the current standard, 'Mt. Barker'.

Organic rotations of corn-soybean, corn-soybean-wheat and corn-soybean-wheat-hay in Maryland showed that longer, more phenologically diverse rotations reduced populations of major annual broadleaf weeds. A comparison of two and four year organic and conventional broccoli, winter squash and cover crop rotations in Maine showed that improvement in soil physical quality increased with the percentage of time in cover crops. Seed bank of the dominant weed, Chenopodium album, was less in the 4-year system that alternated a cash crop with cover crops and fallow relative to a 4-year system in which the two cash crops alternated with two years in a grain/clover sod. Studies in Maine and Pennsylvania are comparing seed bank reduction in rotations of cash crops, various sequences of annual and perennial cover crops, and continuous cultivated fallow.

The project has resulted in thirteen refereed publications, ten book chapters, a PhD dissertation and numerous abstracts and non-refereed papers. A book on crop rotation is close to submission. In addition, the previous project helped leverage three SARE grants: (i) "Optimizing Reduced Tillage Systems for Vegetables Grown in the Upper Northeast" (Mohler), (ii) "Ecologically-based Weed Management: A Manual and Training Program for Farm Advisors" (Mohler and DiTommaso); and (iii) "Sustainable integrated management of weeds and diseases in a cabbage cropping system" (Bellinder and Dillard). The former project also helped in development of a NE Region IPM grant "Threshold-Based Cover Cropping Strategies for Weed Management" (Gallandt, E.R., C. Reberg-Horton, W.S. Curran, D.A. Mortensen, M.E. Barbercheck) and a NFIPME-RESP grant "A Manual and Extension Program on Weed Ecology and Ecological Weed Management" (DiTommaso and Mohler).

Objectives

1. Reduce effective rates of vinegar and clove oil natural product herbicides through better understanding of the effects of weather conditions, OMRI-approved adjuvants, and sensitivities of specific problematic weeds.
   
2. Determine (i) the optimal environmental conditions, and range of effective planting dates for production of weed-suppressive buckwheat and mustard cover crops, (ii) the effects of buckwheat and mustard cover crops on emergence and growth of specific weeds, and (iii) the impact of different incorporation practices on cover crop decomposition, regrowth, and weed suppression.
   
3. Determine how overall soil fertility, Ca:Mg ratio, and micronutrient concentrations affect weed management and the competitive balance between weed and crop species as hypothesized by organic growers.
   
4. Determine the response of various weed species in several developmental stages to burial, uprooting and breakage to optimize timing and type of cultivation for weed control.
   

Methods

Participating states for each objective are listed in Appendix E, and at the beginning of each description of methods for that objective. Each proposed experiment will be conducted once per year for at least two years at each participating location using the same protocol. The protocols for these experiments were developed through conference calls and follow-up correspondence with each participant. Following each year of each experiment, results from each site will be shared at the annual meeting and discussed via conference calls.

Methods for Objective 1. Reducing effective rates of natural product herbicides (Participating states: CA, DE, IL, MI, MN, NC, NY, PA)
(i) Rate response across multiple sites. In field trials at multiple locations, two natural product herbicides (acetic acid and clove oil) applied at four rates will be evaluated for efficacy in controlling important annual weed species. Acetic acid (Fleischmann's 30% White Grain Vinegar) will be diluted as appropriate and applied at 5, 10, 15 and 20% concentrations at 70 GPA (3.5, 7.0, 10.5 and 14.0 gallons ai/A) with a 0.1% Yucca Extract as adjuvant. Matran II (0.46% clove oil) will be applied at 5, 10, 15 and 20% concentrations at 35 GPA (0.8, 1.6, 2.4 and 3.2 gallons ai/A) with 2.5% Humasol as an adjuvant. An untreated control plot will be included for comparison. The high GPA for vinegar allows application at less toxic, and more readily available concentrations than would be possible at a lower GPA. Plots will be arranged in a randomized complete block design with 4 replicates.

Sites within each state will be selected with known populations of at least three of the following four important weed species: Amaranthus spp. (A. retroflexus, A. powellii or A. hybridus), Chenopodium album, Abutilon theophrasti and Setaria spp. Weed species that are not present at a particular site will be sown following soil preparation in a single 1 m row in the center of each plot. When the fastest growing weed species reaches the 4 lf growth stage, herbicides will be applied using a CO2 backpack sprayer. Weed responses by species will be evaluated visually for each target weed species at 5 and 15 d after herbicide application. At 15 d after application, weeds from four randomly placed 1 m2 quadrats per plot will be counted by species, cut at the soil surface, combined into broadleaf and grass categories, dried, and weighed. Air temperature, solar radiation, and relative humidity will be monitored for the duration of the experiment at all sites. Parameters for dose-response relationships (dry wt versus rate of product) will be estimated for each site and herbicide type using regression. Differences in parameters will be evaluated across sites and discussed with reference to differences in environmental conditions following application. Multiple regression analysis will be used where possible (given sufficient range of conditions for a given environmental factor) to evaluate the effects of temperature, relative humidity, and/or solar radiation on the efficacy of each product.

(ii) Effect of organically approved adjuvants. In field trials at multiple locations, approximately 4 organically approved adjuvants in combination with 2-3 natural products will be evaluated for their potential for reducing rates required to control annual weeds. Adjuvants and natural product will be selected based on preliminary greenhouse screening of products that are OMRI-approved or have potential for OMRI approval as of spring 2007. Likely natural product candidates include vinegar, clove oil, citric acid and saline solutions. Potential adjuvants to be tested include Yucca extract (saponins), Humasol, molasses and pinolene. Each natural product will be applied either without an adjuvant, or with one of four adjuvants. An untreated, weedy control plot will be included for comparison. A single relatively low rate of application will be selected for each herbicide based on results from Experiment (i) or preliminary greenhouse testing. Plot size, experimental design, target weed species and data collection will be as described for experiment (i). Data will be subjected to ANOVA to evaluate the effect of natural products and adjuvant on weed ratings and dry weights. Multiple regression analysis will be used where possible (given sufficient range of conditions for a given environmental factor) to evaluate the effects of temperature, relative humidity, and/or solar radiation on the efficacy of each product.

(iii) Effect of environmental factors on efficacy of natural product herbicides. In field trials at multiple locations, the effect of environmental variables on the efficacy of 2-3 natural product herbicides will be evaluated using data from multiple sites applied at three times of day on each of two dates. A single rate of application and adjuvant will be selected for each herbicide based on results from Experiments (i) and (ii). At each location, field sites will be moldboard plowed and disked. Final seed bed preparation (e.g. harrowing) will occur either immediately following disking or 10-15 days later. Natural product applications will occur when the fastest growing weed species reaches the 4 lf stage (approximately 2-3 wks following each seedbed preparation). Natural products on each of those two dates will be applied at either 8 AM, 12 PM or 6 PM. Temperature, solar radiation, and relative humidity data will be taken hourly for 48 hrs following application at each site. Target weed species, experimental design, and data collection will be as described in Experiment (i). Data will be subjected to ANOVA to evaluate the effect of time of day on weed ratings and dry weights. Multiple regression analysis will be used where possible (given sufficient range of conditions for a given environmental factor) to evaluate the effects of temperature, relative humidity, and/or solar radiation on the efficacy of each product.

Methods for Objective 2. Effects of cover crop planting date and method of incorporation on weed suppression (Participating states: CA, DE, KY, FL MI, MN, NY, WV)
(i) Buckwheat planting date and weed suppression. The experiment will compare a buckwheat cover crop with unweeded (weedy) and harrowed (weed free) control treatments, at multiple planting dates at multiple locations. At each location, plots will be arranged in a split-plot block design with four replications. The main plot factor will be planting date, and the subplot factor will be cover crop treatment. For each location, seeding dates will be determined that extend a little beyond anticipated optimal growing conditions for buckwheat. The criteria used for planting date ranges will be (i) soil temperatures of at least 16°C and (ii) at least 5 wks before expected frost or 3 wks before the mean daily maximum exceeds 32°C. For example, for Geneva NY, that time range is 21 May through 25 August and for Davis, CA, that range is 10 April through 5 May and 1 Oct. through 15 Nov. During the range of potential planting dates, buckwheat will be sown at 3 week intervals. Plots will be scaled to fit the equipment at each site. The seed will be drilled 1 in deep in narrow (< 8 in) rows at a rate of 50 lb/acre. Buckwheat and weedy control plots will be flail mowed and lightly incorporated 10 days after buckwheat flowering (approximately 6 wks after seeding). The weed-free control plot will be harrowed at 2-3 wk intervals to control weeds. At 150 degree days (base 10 C) after planting, buckwheat percent ground cover will be estimated using a diagonal transect of 100 points (Colbach et al. 2000), and buckwheat and weed emergence density by species will be evaluated in four randomly placed 1 m2 quadrats per plot. Immediately before mowing, buckwheat height will be measured, weeds counted by species, and the shoots of both buckwheat and weeds will be harvested from the same four quadrats per plot, dried and weighed.

Two hundred degree days (approximately 2-3 wks) following buckwheat mowing, non-buckwheat treatments will be disked and harrowed to simulate standard field preparation for a subsequent wheat or transplanted vegetable crop. The exception to this procedure will occur following the final buckwheat planting in all locations except CA, where field preparation will be delayed until the following spring at the time when an early sweet corn crop would be sown. Emergence will be monitored in four 1 m2 quadrats per plot at 100, 200 and 400 degree days (base 10 C) following field preparation. At the final emergence count, weeds from all quadrats will be cut at the soil surface, separated into broadleaf and grass categories, dried and weighed.

Mean air temperature for the period 10-40 d after planting and daylength 4 weeks after seeding will be used to model the limit of suitable growing conditions for buckwheat. The effects of cover crop treatment (weedy vs weed free vs buckwheat) and planting date on weed emergence and biomass both during buckwheat growth and following buckwheat mowing, will be evaluated using analysis of variance. Regression analysis will be used to relate cover crop biomass to weed suppression using combined data from all sites and planting dates.

(ii) Mustard planting dates and weed suppression. The experiment will be a 2 by 4 factorial with two planting dates as one factor and two mustard genotypes plus weedy and weed free treatments as the other factor. Plots will be arranged in a randomized complete block design with four replications. "Tilney" yellow mustard will be drilled at 10 lb/acre and "Green Wave" brown mustard, with smaller seed, will be drilled at 6 lb/acre. The seed will be planted in narrow rows (< 8 in) with a grain drill at ½ to ¾ inch deep. The two planting dates will vary across sites based on environmental conditions and grower practices. Planting dates will be chosen so that the cover crops could either precede a late planted crop or follow an early harvested crop. In the Northeast and North Central states this would correspond to an early spring planting when fields can first be worked (soil temperature above 5 C at 1 in) and late July when winter wheat would be harvested or a spring crop of snap beans or sweet corn picked. The crucifers will be allowed to grow until flowering just begins on the yellow mustard (approximately 60 days after planting) and then will be shallowly incorporated into soil. At the same time the nonseeded control treatments will be tilled to eliminate any emerged weeds. Data collection for crop and weed emergence, crop percent ground cover, weed and cover crop biomass, and environmental conditions will be as described for Experiment (i). For the fall planting, weed counts following incorporation will be carried out the subsequent spring using the same methods as described above for the final buckwheat planting date. The effects of cover crop and planting date on weed emergence and biomass both during mustard growth and following mustard incorporation will be evaluated using analysis of variance. Regression analysis will be used to relate cover crop biomass to weed suppression using combined data from all sites and planting dates.

(iii) Optimal incorporation practices. The experiment will compare at least three control/incorporation practices (flail mowing alone, light tillage alone, flail mowing + light tillage) on buckwheat and mustard cover crop (i) weed suppressiveness, and (ii) decomposition and (iii) regrowth. Each cover crop type (mustards and buckwheat) will be grown in separate trials. Plots will be arranged in a randomized complete block design with four replications. At each location, buckwheat will be planted on the date typically used for buckwheat grain production, while mustards will be planted at the most promising timing based on Experiment (ii). Plot size, planting methods and incorporation timing will be as described in Experiments (i) and (ii). Immediately prior to incorporation, cover crop height and biomass samples will be taken. Following incorporation, fields will be inspected twice weekly for 300 degree days (base 10 C) to assess whether the residue is sufficiently decomposed for a planter to operate unimpeded. Preliminary investigations of methods for quantifying cover crop decomposition including both physical and chemical (e.g. myrosinase activity assay) measures and will be carried out prior to initiation of this experiment. At approximately 300 degree days following incorporation, weed emergence by species and total weed and cover crop biomass will be assessed from four 1 m2 quadrats per plot. The occurrence of full size buckwheat seed (green or black) on regrown plants will also be evaluated at that time. The effects of incorporation method on weed emergence, cover crop regrowth, and decomposition will be evaluated using analysis of variance.

Methods for Objective 3: Effects of soil nutrients on crop-weed competition and weed management(Participating states: IL, KY, ME, MN, NY).
(i) To test the hypothesis that overall soil fertility affects the competitive balance between weeds and crops, with crops favored at moderate fertility and weeds favored at high fertility, compost will be applied at appropriate points in the crop rotation at 0 and four geometrically increasing rates (e.g. 0.75, 1.5, 3, and 6 ton/A of composted poultry manure). Crop rotation, application rates and type of compost will be appropriate to the location and crops grown. Near weed maturity, and at other times if useful, number and height of weeds present will be measured in four randomly located quadrats per plot. Quadrats will span from center of one inter-row to the next and be 0.5 or 0.25 m2, depending on weed density. Relation of crop yield, weed size and weed abundance to application rate will be analyzed by regression.

(ii) A field experiment and a pot experiment will test the hypothesis that Ca:Mg ratio affects weed control and weed growth, respectively. In the field experiment, soil tests will be used to determine current pH, CEC, and base saturation ratios. The experiment will compare no amendment versus amendment with either calcite (on low pH soils) or gypsum (on high pH soils) to shift the Ca:Mg ratio toward the Albrecht ratio. Following standard organic practice, amendments will be made incrementally over several years until the desired ratio is achieved. The entire site, or 2 x 5 m subplots within each plot, will be seeded with C. album, a Brassica species, and a Setaria spp. at the beginning of the experiment. A crop rotation typical of organic farms in the region will be followed. The crops will be cultivated in an appropriate manner that includes sweep cultivation. Locations of four 0.5 m2 quadrats that span from one inter-row center to the next will be marked in the row with a stake in each plot. Weeds in these quadrats will be censused by species and growth stage before and after cultivation events. Proportion of weeds surviving will be subjected to multivariate analysis of variance followed by univariate ANOVA for each species.

In the pot experiments, three to five weed species, including those listed above, will be pre germinated and sown in pots containing an acidic field soil that has been unamended, amended to neutral pH with dolomitic lime (low Ca:Mg ratio), amended with an appropriate mixture of dolomite and calcite to achieve the Albrecht ratio, or amended with calcite to achieve a high Ca:Mg ratio. To improve aeration and drainage in the pots, the field soil will be amended with vermiculite and peat prior to soil testing and Ca:Mg adjustment. Plants will be harvested at 45 days after planting, oven dried, and dry weights subjected to ANOVA to test for effects of base ratio on each weed species.

(iii) A greenhouse replacement series trial will be used to test the hypothesis that micronutrient supplementation improves competitive ability of crops relative to weeds as postulated in the popular organic farming literature. Field soil from organically farmed fields that have not received micronutrient amendments will be mixed with peat and vermiculite to assure water holding capacity under greenhouse conditions (4 parts field soil:1 part peat: 1 part vermiculite). Pots will either receive no amendment or a commercial organic micronutrient supplement. Seedlings will be thinned to two plants per pot prior to onset of competition: two crop plants, one individual of a crop and one of a weed, or two weed plants. Crops will include tomato, lettuce, soybean and any other species of special interest to particular investigators. Weeds will be species appropriate to the specific crops and regions. Plants will be harvested after 6 to 8 weeks, dried and weighed. Data will be analyzed by standard replacement series methods. If competition between particular crops and weeds is affected by supplementation, additional experiments will determine the particular micronutrients mediating the interaction.

Methods for Objective 4. Causes of weed mortality during cultivation (Participating states: CA, DE, IL, KY, MN, NC, NY)
(i) Causes of mortality by tine weeding of seedlings in the white thread stage. This experiment will examine the relative importance of the principal factors whereby tine weeding kills weed seedlings in the white thread (pre-emergence) growth stage: breakage and desiccation due to loosening of soil-root contact. The experiment will use a two-factor randomized split-plot design with 4 replications. Main plots will be tine weeded or not tine weeded. Sub-plots will be watered immediately after tine weeding and twice daily during the first 48 hours after tine weeding or not. Watering will give live seedlings a chance to regenerate root hairs. To ensure a uniform seed bank of non-dormant seeds, 800 seeds/m2 each of hairy galinsoga, velvetleaf pre-treated to break dormancy, and a non-dormant seed lot of Powell amaranth will be sown in strips 3 m by 1 m within main plots at crop planting. Watered and unwatered 0.5 m2 quadrats will be centered in these strips, separated by 1.5 m. Seedlings will be counted and removed from quadrats for 5 days after tine weeding which is sufficient time for emergence of weeds that are already in the white thread stage.

Difference in counts between tine weeded and non-tine weeded plots will indicate total mortality due to tine weeding. Difference between watered and unwatered tine weeded plots will indicate number of seedlings that would have died due to desiccation. Difference between watered and unwatered plots that were not tine weeded will indicate additional emergence due to watering and will be used as a correction factor. At some locations the experiment will be set up as subplots within a larger experiment by either protecting some parts of the macro-plots from tine weeding with a board fastened to the soil or by picking up the tine weeder for a short distance.

(ii) Degree and types of damage to emerged weeds by soil covering. Sub-plots will be established in cultivated plots by sowing seeds as in (i) above at planting and at 5 to 7 day intervals after planting. Just before the first row crop cultivation when soil will be thrown into the crop row and/or at a tine weeding, the number and size of emerged weeds will be assessed in each quadrat. The cultivation operation will then be performed. Then weeds that are showing will be scored for percentage burial, after which the quadrats will be carefully excavated to determine the number of buried and partially buried weeds that were also physically damaged. Degree of burial and physical damage will be evaluated for each species by regression against height of the plant.

(iii) Interactions between weed species, weed size and types of disturbance. Weeds of several species will be grown to various sizes in small field plots or flats in a glass house. The first trial will assess weed susceptibility to burial. In this trial, plant shoots will be carefully bent into a horizontal position in the late afternoon when plants are relatively flaccid, and buried with loose soil to simulate burial by cultivation The percentage of plants recovering from this treatment within two weeks will be recorded and values regressed against plant size. Difference in species response to burial will be assessed by comparison of regression curves.

The second trial will assess weed susceptibility to uprooting. Weeds of several species will be grown to various sizes in deep flats, and be pulled up 0% (control), 25%, 50% or 100% of their shoot height, or completely uprooted and left on the soil surface. Soil moisture at time of treatment will be suitable for cultivation (i.e., slightly moist). Flats will either be immediately watered or not, and watered flats will continue to be watered daily. Unwatered flats will be allowed to dry for 2, 4, or 8 days and then all flats will be watered daily thereafter. Plant survival and mass of surviving plants will be scored after two weeks. Relative susceptibility of various species to uprooting under wet and drying conditions will be evaluated by regression of percentage survival and mass of surviving plants against degree of uprooting treated as an ordinal variable.

Measurement of Progress and Results

Outputs

• Recommendations on optimal rates, adjuvants and weather conditions for effective use of acetic acid and clove oil as herbicides; information on sensitivities of various weed species at several stages of growth.
• Recommendations on optimal planting dates and incorporation practices for effective use of buckwheat and mustard cover crops in suppressing specific problematic weeds; Information on the effective planting windows for these cover crops throughout the U.S.
• Information that will help farmers balance the costs and benefits of adjusting base saturation ratios and micro-nutrient levels; evidence that excessive application of compost does not benefit the crop but can hinder weed management.
• Recommendations on cultivation timing relative to weed size; information that will help growers adjust cultivator action to target specific species and growth stages.

Outcomes or Projected Impacts

• Natural product herbicides will be widely used to reduce reliance on hand weeding and cultivation in organically produced crops, with consequent reductions in tillage and costs of production.
• At present, cover crops are used primarily for nitrogen fertility and improved soil quality. Due to the project, cover crops will be more widely used in sustainable agricultural systems to reduce weed pressure, with consequent reduction in tillage, cultivation and hand weeding, and improved weed control and crop yield.
• Due to the project, high calcium lime, gypsum and micronutrient supplements will be used where needed but not otherwise, with consequent cost savings. Over-application of compost will be reduced, with consequent cost savings to the grower and reduced impacts on water resources.
• The project will improve the efficiency and effectiveness of cultivation for weed control, with consequent improvements in yield and savings in labor and fuel.

Milestones

(2007): Objective 1: Initiation of rate response trial. <br>Objective 2: Initiation of buckwheat planting date study. Preliminary testing of methods of quantifying buckwheat decomposition. <br>Objective 3: Initiation of compost rate studies. Initiation of cation ratio field studies. First greenhouse cation ratio and micronutrient trials. Collection of preliminary data. <br>Objective 4: First tine weeding and soil covering experiments. First weed burial experiments. Evaluation of experimental protocols and possible modification.

(2008): Objective 1: Refinement and repetition of rate-response trial. Preliminary screening of OMRI-approved adjuvants in greenhouse. Initiation of adjuvant field trial. <br>Objective 2: Refinement and repetition of buckwheat planting date study. Initiation of mustard planting date study. Preliminary testing of methods of quantifying mustard decomposition. <br>Objective 3: Continuation of compost rate and cation ratio field trials. Evaluation of whether these field experiments should be modified. Repetition of cation ratio and micronutrient greenhouse trials. Evaluation of whether the data from the greenhouse trials are conclusive. <br>Objective 4: Refinement and repetition of tine weeding and soil covering experiments. Repetition of weed burial experiment and extension to additional species.

(2009): Objective 1: Continuation of adjuvant study. Refinement of methodology for environmental factor study based on results of rate-response trial. Write up results from rate response trials. Begin outreach based on findings to date. <br>Objective 2: Continuation of mustard planting date study. Write up results from buckwheat planting date study for publication. Initiation of buckwheat incorporation study. Begin outreach based on findings to date. <br>Objective 3: Continuation of compost rate and cation ratio field trials. Write up results from greenhouse cation ratio and micronutrient experiments if they are conclusive. Modified or additional micronutrient greenhouse trials. Begin outreach based on findings to date. <br>Objective 4: Repetition of tine weeding and soil covering experiments or development of "second generation" experiments. Write up weed burial data for publication. Begin weed uprooting experiments. Begin outreach.

(2010): Objective 1: Continuation of environmental factor study. Write up results of adjuvant study for publication. Continue outreach. <br>Objective 2: Continuation of buckwheat incorporation study. Write up results from mustard planting date study for publication. Continue outreach. <br>Objective 3: Continuation of compost rate and cation ratio field trials. Repeat the "second generation" micronutrient greenhouse trials. <br>Objective 4: Continue tine weeding and soil covering experiments. Repeat uprooting experiments.

(2011): Objective 1: Write up results of environmental factor study for publication. Continue outreach. <br>Objective 2: Write up of results from buckwheat incorporation study. Continue outreach. <br>Objective 3: Write up compost rate and cation ratio field trials and "second generation" micronutrient trials for publication. Continue outreach. <br>Objective 4: Write up studies for publication. Continue outreach.

Projected Participation

View Appendix E: Participation

Outreach Plan

Experiment station trials will be presented at well-advertised field days. When on-farm trials have particularly interesting results, twilight meetings will be organized to present the results to growers. Researchers will give talks on project results at cooperative extension training sessions and grower conferences (e.g., state organic farming association meetings, regional vegetable growers association meetings etc.). Results will also be presented in extension newsletters and newsletters of state organic farming associations. Peer reviewed articles will be published on the research, and results presented at meetings of the Weed Science Society of America and the regional weed science societies.

Organization/Governance

The project will be executed by a Technical Committee made up in the manner described in the Guidelines for Multistate Research Activities. The officers consist of a chair and secretary who are elected by the committee annually. The committee will meet yearly in conjunction with the annual meeting of the Weed Science Society of America. Sub-committees focused on particular objectives will confer as needed by teleconference.

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Attachments

Land Grant Participating States/Institutions

CA, FL, KY, ME, MI, MN, MS, NH, NY, WV

Non Land Grant Participating States/Institutions

Kentucky State University, The Royal Veterinary and Agricultural University