Dollar spot is one of the most common diseases turfgrass managers face during the growing season. It is a foliar disease that impacts both warm-and-cool season turfgrass around the world. Colonial Bentgrass and Creeping Bentgrass 'Crenshaw' and 'Penncross' are some of the more susceptible cool-season cultivars. Some of the susceptible warm-season turfgrasses include Seashore Paspalum, Bermudagrass, and Zoysiagrass.
Depending on the turfgrass and management type (golf course, sports field, or home lawn), dollar spot can cause varying degrees of turfgrass damage from [blighted, discolored leaf blades] in home lawns, to severe scarring on golf course putting greens. In these situations, dollar spot can disrupt the overall aesthetics of turfgrass and have a negative impact on the playability of surfaces by causing scarring.
The causal agent for dollar spot is the Clarireedia species, formerly known as Sclerotinia homeocarpa. The overwintering structures (mycelium) of Clarireedia species begin active growth when days are warm and humid and evenings are cool resulting in heavy dew. Peak dollar spot activity occurs when temperatures are 60 - 84°F with prolonged humidity. Dollar spot is unique in that, while the turfgrass canopy needs moisture for infection, dollar spot is more severe in dry soils. Turfgrass that is deficient in nitrogen is also more susceptible to dollar spot. This disease can impact cool-season turfgrass throughout the growing season. For warm-season turfgrass, dollar spot primarily occurs in spring or fall.
Symptoms and Identification
Dollar spot is a foliar disease resulting in blighted leaf blades. Symptoms for this disease may look different depending on mowing height. For higher cut turf, initial symptoms begin as small tan-colored lesions with red to maroon margins often expanding across the leaf blade. In some cases, the lesions may have an hourglass appearance. Infected areas can range from 1 - 12 inches in diameter. In lower cut turf, symptoms first appear as circular tan spots approximately 1 inch in diameter, but these spots can coalesce into larger infected areas. One of the telltale signs of dollar spot is the presence of white mycelium on the leaf blades in the morning after heavy dew.
If feasible, select a turfgrass variety less susceptible to dollar spot. Proper nitrogen fertilization will aid in turf recovery by stimulating new leaf growth. Maintaining adequate fertility and proper irrigation throughout the growing season will produce a more vigorously growing turf. Cultural practices focusing on thatch management will reduce organic matter buildup as well as aid in decreasing dollar spot severity. Reducing time of leaf wetness can significantly minimize spread and dollar spot development. Adjusting irrigation times to early morning, removing morning dew by mowing, dragging, or rolling are methods that can reduce canopy wetness.
Preventative applications are the most effective strategy for successful dollar spot control. Under higher disease condition, shorter application intervals and higher fungicide rates should be used. It is important to use between 1 - 2 gal/1000 sq ft spray volume for effective coverage. There are documented cases of fungicide resistance with dollar spot. Designing a fungicide program that rotates modes-of-action will reduce the risk of resistance development.
Rayora® Fungicide is a next generation DMI fungicide containing the active ingredient flutriafol which is excellent for preventative and curative dollar spot control. Preventative dollar spot control is achieved with Rayora using 14 (on greens) to 21-day application intervals at 1.4 fl oz per 1,000 sq ft.