Turfgrass landscapes cover approximately 50 million acres of land in the United States and provide numerous environmental, recreational, and economic benefits (Beard and Green, 1994; National Turfgrass Federation, 2009).  The 14,000+ golf courses present in the U.S. only account for approximately 5% of the total turfgrass area; however, the golf industry is estimated to contribute over $84 billion to the U.S. economy (We Are Golf, 2018).  The intensive practices required to maintain putting greens, fairways, and tee boxes on a golf course can make the turfgrass in these areas susceptible to a number of disease, insect, and weed pests that can have a significant economic impact on golf course management.  

Dollar spot is caused by a group of fungal species from the newly formed genus Clarireedia (Salgado-Salazar et al. 2018). These fungi infect the leaves of turfgrass plants and causes severe blighting of the foliage in roughly circular infection centers 2 to 5 cm in diameter. Optimal environmental conditions for dollar spot development include temperatures between 15 and 30°C, humidity in excess of 85%, and prolonged periods of leaf wetness (Smiley et al. 2005). When optimal infection conditions persist, numerous dollar spot infection centers can appear and blight a large area of turf in just a few days.  Infection can progress into the plant crown and cause plant death, which leaves sunken depressions in the turf stand detracting from the playability and/or aesthetic value of the affected turf. Nearly all grass species that are grown for turf are susceptible to Clarireedia infection, and those commonly found on golf courses such as creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua) are particularly susceptible (Smiley et al. 2005).  In addition, the optimal conditions for dollar spot symptom development (temperatures between 15 and 30°C and high humidity/prolonged leaf wetness) are common in many temperate areas of the U.S. from May until October.

The prolonged period of optimal conditions for dollar spot development in many temperate climates typically require 10 or more fungicide applications in a single season to obtain complete control of this disease.  Despite the resources employed to control dollar spot, relatively little is known about the basic biology and epidemiology of the Clarireedia spp. that cause this disease.  As a result, integrated dollar spot management plans have been largely ineffective and superintendents rely almost exclusively on chemical approaches for acceptable disease control.  However, numerous biological, economic, and environmental concerns have arisen in recent years following decades of reliance on fungicides.  From a biological standpoint, Clarireedia develops resistance to fungicides very quickly, and over-reliance on chemical control has led to reported resistance to the benzimidazole, demethylation inhibitor, dicarboxymide, and succinate dehydrogenase inhibitor fungicide classes (Golembiewski et al. 1995; Sang et al. 2015). From an economic standpoint, many golf facilities across the country struggle to afford the season-long fungicide programs required to control this disease. Finally, societal and regulatory pressures have led to an increasing desire to use fewer chemical inputs in golf course management and fewer newer turfgrass fungicides coming to the market (Pimental et al. 1992; Tomer et al. 2015).  These significant concerns indicate that there is an urgent need for multi-disciplinary/institutional collaborative research that will produce new and more sustainable dollar spot control strategies.  

Need as indicated by stakeholders. In February 2018, a broad group of representatives met in San Antonio, TX as part of North Central Development Committee Project 232.  The group included university and government researchers representing turfgrass pathology, breeding, physiology and management, as well as industry stakeholders including a representative from the United States Golf Association (USGA). This group indicated that dollar spot was one of the most important and costly diseases for turfgrass managers to manage on golf courses around the world. This need as indicated by the stakeholders led to the creation of NC1208, which has been in place since 2019. The NC1208 group has been effective at addressing many of the stated objectives in that project, particularly given the disruption of the COVID-19 pandemic, and currently has 1 project completed and in manuscript preparation, another project complete and in preparation for an extension publication/fact sheet, and 3 other ongoing projects. Despite our productivity, dollar spot severity continues to increase around the world as a result of climate change, particularly in Europe and Scandinavia where chemical control is severely limited. If funded for another 5 years NC1208 will continue ongoing research projects related to increasing adoption of best management practices, use of resistant bentgrass cultivars, and implementation of disease predictive modeling. The team has also discussed new projects related to improving the efficacy of biocontrol, harnessing the turfgrass microbiome to suppress the dollar spot pathogen, and novel cultural practices and fungicide alternatives for dollar spot suppression. Over the next 5 years we will have a greater understanding of the pathogen’s biology that will foster improved cultural, chemical, and biological management strategies to meet the increasing threat that dollar spot poses to amenity turf around the world.

The importance of the work and what the consequences are if it is not done. Dollar spot is the most commonly observed disease of turfgrasses on golf courses throughout the world.  Approximately 70% of U.S. golf course superintendents in the Midwest and Northeast consider dollar spot to be their primary disease, and the average golf course superintendent in these regions spent approximately $15,000 and $28,000, respectively, to control dollar spot in 2016 (Hirvela, personal communication).  In the U.S., more fungicide is used and more money is spent to control dollar than any other turfgrass disease on golf courses (Hirvela, personal communication).  If the above work is not conducted, it is likely that golf course superintendents will remain heavily reliant on chemical control of dollar spot and that new cases of fungicide resistance will continue to be reported.  This will be financially disadvantageous to the golf course facility and may result in more rapid development of multi-class fungicide resistant populations of Clarireedia and increasing concerns surrounding the non-target impacts of fungicide usage on human and environmental health.

The technical feasibility of the research: The scientific team assembled for this project includes approximately two-dozen university and government researchers representing all geographic areas of the United States except for the arid southwest where dollar spot is rarely observed.  The team has expertise in all areas related to the stated priority areas: applied and molecular aspects of turfgrass pathology, breeding, management, physiology, and genetics.  Nearly every project member has experience researching dollar spot in some capacity and over half of the members have over 10 years of experience working with this disease and have published numerous peer-reviewed research articles on the subject.  In addition, nearly all members reside at land grant institutions and have the field and/or laboratory resources at their respective institutions needed to actively contribute to their area of the project.  Many project members have appointments in Cooperative Extension and can use their appointment to successfully communicate and disseminate project results out to the broader turfgrass community. Lastly, the team has been highly productive in conducting coordinated research over the first 5 years of NC1208 and has numerous additional research projects in development if the project is to receive an additional 5 years of funding.

The advantages for doing the work as a multistate effort: Dollar spot is one of the few turfgrass diseases that commonly occurs on multiple turfgrass species, including both warm-season and cool-season turfgrasses. However, many attributes of the pathogen and methods for managing the disease differ between geographic regions.  For instance, research published in early 2018 indicated that different species of Clarireedia are present on warm vs cool-season turfs but produce similar disease symptomology (Salgado-Salazar et al. 2018).  In addition, regional environmental conditions result in higher pressure, and more fungicide required, in certain regions relative to others. The higher fungicide usage on certain turf species and in certain regions has led to more rapid development of resistant populations of Clarireedia relative to other regions and species, with important regional ramifications for control.  Dollar spot is a common turfgrass disease with a broad geographic range and numerous unique regional characteristics, making it an ideal candidate for multi-state collaboration.

What the likely impacts will be from successfully completing the work: Dozens of individual researchers have conducted dollar spot research since the pathogen was first characterized in the United Kingdom in 1937 (Bennett 1937).  While significant progress has been made during the first 5 years of the NC1208 project, our collaborative research needs to continue to provide the greatest benefits to the turfgrass industry. Coordination will reduce redundancy, provide additional testing sites for research, and foster the continuation of collaborative research projects that can be used to obtain additional research funding and speed the development of effective best management practices for the control of this disease with fewer chemical inputs. Specific impacts if we are to receive support for the next five years include, (1) establishment of best management practices for dollar spot control in each region of the country, (2) development of an extension publication/fact sheet describing how best to implement dollar spot-resistant cultivars into existing stands AND how best to manage them using fewer chemical inputs, and (3) creation of a central dollar spot website that can serve as a single, science-based resource for dollar spot management for practitioners all around the world. Surveys of golf course superintendents will be conducted in year 1 and again in year 5 of the new project to assess potential adaptation of recommendations and to document potential economic impact of the team’s recommendations.