First Report of In Vitro Insensitivity to Fluazinam of Clarireedia jacksonii Causing Dollar Spot of Turfgrass on New England Golf Courses

Dollar spot, caused by the newly renamed ascomycete fungus Clarireedia spp., contributes to the aesthetic and functional damage and ultimate death of turfgrass. Fluazinam, a protective fungicide belonging to the 2,6-dinitroaniline chemical group, has proven to be one of the most efficacious fungicide classes of managing a variety of turfgrass diseases, including dollar spot, due to its low risk for fungicide resistance as a broad-spectrum fungicide. Dollar spot isolates collected from six New England golf courses with suspected resistance to multiple fungicide classes had shown reduced sensitivity to fluazinam using a mycelial growth inhibition assay. This is the first report of reduced sensitivity to fluazinam in dollar spot field isolates in the United States. Briefly, in vitro sensitivity assays of 22 isolates collected from 12 golf courses and UMass turf research facilities showed that reduced fluazinam sensitivity of isolates was detected on six golf courses since 2017, demonstrating that fungi with higher exposure to fluazinam tend to develop reduced sensitivity over time. To date, there is no reported field resistance of fluazinam in C. jacksonii. However, the findings highlight the need for ongoing monitoring of in vitro and field sensitivity to fluazinam in C. jacksonii, as well as emphasizing judicious use of fluazinam in managing dollar spot disease to delay the development of fungicide resistance.