Dollar spot is caused by the fungal pathogen Sclerotinia homoeocarpa, The pathogen blights leaf tissues but does not affect turf grass roots or crowns. The disease is a common concern on golf course turf, but is rare in sports turf and professional landscapes. Disease symptoms commonly result in poor turf quality and appearance
HOST PLANTS: Common in Dollar spot is most commonly found on closely mowed turfgrasses. The pathogen infects most cool and warm-season grasses throughout the world, including creeping bentgrass, annual bluegrass , Kentucky bluegrass , perennial ryegrass , hybrid bermudagrasses , seashore paspalum (Paspalum vaginatum), and zoysiagrass
SYMPTOMS: On fine textured and close-cut turf, the disease appears as round, brown to straw-colored and somewhat sunken spots approximately the size of a silver dollar; thus, the common name "dollar spot". In coarse textured grasses maintained at taller cutting heights, the dead spots are larger and more diffuse. Dollar spot is readily distinguished by characteristic lesions on the leaf blades of live plants near the border of the affected area. Lesions are light tan with a reddish-brown border, and usually radiate from the margins of the leaf blade. On fine bladed grasses such as bentgrass, the lesions usually girdle the leaf blade.
Damage is usually more severe if there is a deficiency of nitrogen. If the turf is examined when the disease is active early in the day before the dew dries, cobweb-like mycelium of the fungus can be seen growing on affected areas. During early stages of the disease, affected plants may appear water-soaked and wilted, but spots quickly fade to a characteristic straw color.
FAVORED ENVIRONMENT: Disease fungi are spread from one area to another by water, wind, mowers, other equipment or shoes. This fungus is capable of growth over a wide range of temperatures (50° to 90°F), but disease development is greatest at temperatures between 70° and 80°F. The dollar spot fungus survives unfavorable temperature and moisture conditions in plant tissue and thatch as dormant, compact masses of mycelium, called sclerotia. Low nitrogen and potassium levels in the soil have been reported to increase the severity of dollar spot.
DOLLAR SPOT CONTROL: Mow lawns at the recommended maximum height. Try not to cut more than 1/3 of the leaf surface in any one mowing, and if possible, clean the mower between cuttings with a 10% bleach solution. Remove excess thatch and aerate compacted dirts. Improve drainage by top-dressing with organic matter, such as compost or well-aged animal manure. Keep lawns well watered, but avoid sprinkling in the late afternoon or evening. Do not over water. You may apply a slow-release organic fertilizer high in nitrogen; applying liquid seaweed and chelated iron is also helpful. Don't overfertilize, since this can result in an increase of other turf grass diseases, such as brown patch. Avoid night watering or other irrigation practices that allow the leaves to remain wet for long periods. Over seed in fall with resistant cultivars. Dollar spot is rarely serious enough on home lawns to require fungicide treatments.