Text adapted from Turfgrass Pest Management: A Guide to Major Turfgrass Pests in Oklahoma. Oklahoma Cooperative Extension Service.

CAUSE: Dollar spot is caused by species of the fungi Moellerodiscus and Lanzia (formerly Sclerotinia homoecarpa).

HOSTS: Bentgrass, bermudagrass, bluegrass, ryegrass and zoysiagrass.

SYMPTOMS: Small circular areas of turfgrass about two inches in diameter are affected (Figure 1). Spots may merge to form large, irregular areas. Individual infected leaves develop a lesion that is first chlorotic, then water-soaked and finally a bleached straw color. Dollar spot lesions are characteristically bounded by a tan to reddish brown margin, and they generally extend across the entire leaf blade (Figure 2). When dew is present on grass blades and the pathogen is active, a white cottony growth of the fungus may be seen on diseased turfgrass (Figure 3).
Spots in sod-forming grasses, such as bentgrass and bermudagrass, usually disappear once the disease is controlled; however, spots in bunch-type grasses, such as ryegrass, often remain because of their inability to fill in the damaged areas.

DISEASE CYCLE: The dollar spot fungi survive unfavorable periods by going dormant in infected plants. Under favorable environmental conditions, the dormant fungi resume growing on foliar tissues and out into the humid air. Whenever the fungi contact moist leaf surfaces, they can penetrate the leaf and cause infection.

FACTORS FAVORING DISEASE DEVELOPMENT: Dollar spot develops most rapidly during warm, moist weather in spring and autumn when heavy dew occurs. It can continue to develop during humid weather throughout the summer. Nitrogen deficient turf, turf with excess mat or thatch, and plants growing in dry soils with high moisture levels around the leaves from dew or frequent irrigation are more prone to dollar spot.

CONTROL: Maintain adequate to high nitrogen fertility during periods of dollar spot activity. Reduce prolonged leaf wetness and prevent dry soils by watering deeply but infrequently. Avoid late afternoon and evening watering and remove morning dew by irrigating lightly in the early morning. Promote good air circulation over the turf by pruning or removing trees or shrubs and removing other barriers.
Remove excess thatch by power raking to reduce the potential for reinfection. Golf greens should be regularly core cultivated and topdressed to reduce thatch buildup.
Many fungicides are available for dollar spot control. The fungicides are most effective if they are alternated and applied in the early spring and autumn before disease develops, and when used in conjunction with good turfgrass management practices.

Figure 2. -- "Straw-colored dollar spot lesions with reddish brown margins", Courtesy of C.S.S.A.

Figure 3. -- "Cottony mycelium of dollar spot fungus", Courtesy of C.S.S.A.