Working with problem areas
Description of the disease
Dollar spot affects small, circular areas of turf, about 1" — 5" in diameter. Spots may merge to form large, irregular areas. Leaves appear water-soaked initially, then brown and often exhibit a reddish band extending across the leaf. Lesions on leaves often have a distinctive "hourglass" shape with necrosis on the outer edges of the leaf blade and healthy tissue in the middle. Fine, white, cobwebby hyphae (fungal threads) may be seen in early morning. The fungus survives as mycelia or stromata (dark, tiny, hard, resting bodies) on plants or in plant debris during periods of unfavorable weather conditions.
Bentgrass, bermudagrass, fescue, ryegrass and annual bluegrass can be affected, but closely mowed grasses of any of these species are most susceptible to the disease.
Conditions favoring this disease
Dollar spot is most common during the spring and fall months in California, especially on annual bluegrass, Kentucky bluegrass, and creeping bentgrass used in coastal plantings. Disease development is favored by moderate temperatures (60° — 80°F) with high relative humidity. Excessive leaf wetness and fog contribute to disease development as do water stress and excess thatch development. Dollar spot is primarily a problem on golf courses and lawn bowling greens.
Proper fertilization and irrigation as well as adding compost are important in preventing the development of dollar spot. Fungicides may be necessary to provide control if the disease develops.
Turfgrass deficient in nitrogen tends to develop more dollar spot than turfgrass adequately fertilized. Apply recommended amounts of nitrogen and maintain adequate air circulation. Keep thatch to a minimum. Irrigate based on evapotranspiration needs of the turfgrass to a depth of 4"— 6", but avoid creating drought stress by extending the interval between irrigations too long. Raise the mowing heights as much as possible.
Avoid prolonged leaf wetness by irrigating in the morning or early afternoon rather than later in the day. Remove morning dew with a light irrigation or poling. Poling involves dragging the surface of the turf with a long bamboo or plastic pole, or with an irrigation hose, to remove the dew from the grass leaves. Some varieties of creeping bentgrass show higher levels of tolerance to this disease than others. Varieties such as Putter, Emerald, Forbes 80-12, SR-1020, Penneagale, Penncross, Century and Crenshaw are quite susceptible to dollar spot, while varieties such as L-93, A-1, Providence and Pennlinks have shown tolerance to this disease.
Adding composted top dressings has been shown to reduce the incidence and severity of dollar spot, allowing a reduction in the frequency and/or application rates of fungicides.
Apply fungicides when environmental conditions favor the development of the disease, or when the first symptoms are detected. Apply until environmental conditions are no longer favorable for the disease.