NCDC232: Biology, Etiology, and Management of Dollar Spot in Turfgrasses
(Multistate Research Coordinating Committee and Information Exchange Group)
NCDC232: Biology, Etiology, and Management of Dollar Spot in Turfgrasses
Duration: 12/04/2017 to 09/30/2019
Statement of Issues and Justification
Dollar spot, caused by the fungus Sclerotinia homoeocarpa, is the most common and important turfgrass disease worldwide. This pathogen infects all grass species that are grown for turf and develops across a broad range of climatic conditions. In the United States, 42% of turfgrass managers list dollar spot as their primary disease problem, and approximately 35% of fungicides applied to turf are for control of this disease.
The dollar spot pathogen initially infects the leaves of turfgrass plants, causing severe blighting of the foliage in discrete infection centers up to 6 inches in diameter. Over time and under ideal environmental conditions, infection progresses into the plant's crown and causes death, leaving a sunken depression in the turf stand that detracts from the playability and/or aesthetic value of the affected turf. In many areas of the U.S., weather conditions are favorable for dollar spot development throughout most of the growing season. During periods of intense disease activity, stands of susceptible turf can be severely damaged by dollar spot in a short period of time.
Dollar spot was first described in 1937 by F.T. Bennett working in the U.K. He isolated the pathogen into pure culture, proved its pathogenicity and observed the sexual stage of the fungus. Based on his observation of sclerotial structures in pure culture, Bennett placed this pathogen in the Family Sclerotiniaceae and in the Genus Sclerotinia. However, soon after publishing of Bennetts description of S. homoeocarpa, numerous investigators questioned the taxonomic classification of this pathogen. The proper taxonomic standing of this important turfgrass pathogen remains unknown still today given that the fungus that is routinely associated with disease symptoms does not produce any spores (sexual or asexual) and produces substratal stroma rather than sclerotia. Based on these observations and phlyogenetic analyses, most support the notion that the proper taxonomic placement of this pathogen is in the Family Rutstroemiaceae.
Despite the global significance of dollar spot, relatively little is known about the basic biology and ecology of S. homoeocarpa and its interactions with turfgrass hosts. Researchers are just starting to understand some of the most fundamental aspects of this pathosystem, such as the correct taxonomic placement for the pathogen and how the pathogen initiates infection within the turf host. If we are to develop and implement integrated pest management strategies, serious strides in our understanding of the basic biology, ecology and epidemiology of the dollar spot pathosystem are needed.
Due to our lack of knowledge about the dollar spot system, it is impossible to develop management plans that are truly integrated. Most turfgrass managers rely solely on chemical approaches to manage the disease, applying fungicides every 14 to 21 days when disease activity is observed. This approach is not sustainable from a biological, economical, environmental and health standpoint. First, from a biological standpoint, S. homoeocarpa develops resistance to fungicides very quickly, and over-reliance on chemical control has led to widespread multiple resistance in pathogen populations. Second, from an economic standpoint, the turfgrass industry has been severely affected by the economic downturn and many facilities can no longer afford chemically-based strategies for dollar spot control. Finally, from an environmental standpoint, the chemical options for control of dollar spot control are dwindling rapidly due to environmental and human, animal and wildlife health concerns and federal/state/local regulations.
A group of plant pathologists and turfgrass scientists with interest in dollar spot and S. homoeocarpa met in June 2009 in conjunction with the 14th International Sclerotinia Workshop in Wilmington, NC. The group was comprised of scientists with a diversity of backgrounds, including plant breeding, biological control, genomics, epidemiology, disease forecasting, economics, population biology, turfgrass management, molecular plant-microbe interactions, and fungicide resistance. Our discussions centered on building collaborative relationships across Universities and establishing a USDA regional project to foster these collaborations.
The primary benefit of this regional project is the breadth and depth of expertise within the group of scientists, which cannot be found in any one institution. This diversity of expertise will enable the group to develop and implement multi-disciplinary research projects that would not be possible within a single institution or smaller groups of collaborators. In these times of shrinking state budgets, a regional collaborative project provides faculty with the opportunity to share resources and expertise that may not be available at every institution.
The areas of emphasis identified by the group for collaborative research were integrated management, host-parasite interactions, epidemiology, and population dynamics. Research in the area of integrated management is being conducted at Penn State, Mississippi State, and the University of Maryland. They will investigate the effects of common turf cultural practices on dollar spot activity. The influence of timing and application techniques on fungicide performance will be evaluated in an effort to maximize the performance of chemical applications. In addition, novel approaches for dollar spot management will be sought, including biological control agents, suppressive soils, and hypovirulent strains.
The interactions among S. homoeocarpa and its turfgrass hosts are being researched at The Ohio State University and NC State University. These researchers are sequencing the S. homoeocarpa genome in collaboration with the Venter Institute. At the same time, libraries of Expressed Sequence Tags are being generated and sequenced for studies of the plant and fungal genes involved in pathogenicity and resistance. A broad range of potential hosts are being inoculated with isolates of S. homoeocarpa from cool- and warm-season turfgrasses. Compatible and incompatible interactions will be studied microscopically in an effort to determine which steps in the infection process determine host specificity. This knowledge is expected to assist plant breeders in the development of turfgrass varieties with improved resistance to dollar spot, either through traditional or molecular breeding techniques.
Researchers at the University of Wisconsin, Oklahoma State University and The Ohio State University are focusing on the epidemiology of dollar spot. They are developing environmental models for prediction of disease outbreaks by monitoring dollar spot activity in multiple locations. Such a model would be expected to assist turfgrass managers in the proper timing of preventive fungicide applications for dollar spot. These researchers are also evaluating the effectiveness of early-season fungicide applications, which has been shown to substantially delay dollar spot epidemics in other locations. Finally, these researchers are investigating the growth and survival of S. homoeocarpa in soil and thatch.
Researchers at NC State University, Rutgers, University of Massachusetts, and University of Guelph are focusing their efforts on the dynamics of S. homoeocarpa populations. Projects within this group are focusing on the correct taxonomic placement for this pathogen, the genetic structure of pathogen populations worldwide, the evolution of fungicide resistance in S. homoeocarpa populations, and the spread of dsRNA viruses that lead to development of hypovirulent strains.
Upon the successful completion of this project, we expect to have a basic understanding of the dollar spot pathosystem that will assist in the development and implementation of integrated management plans for turfgrass managers. In addition, the collaborative network of turfgrass scientists assembled for this project will significantly enhance the likelihood for securing future extramural funding on this and other important turfgrass pathogens.
To develop a full proposal for submission.