What To Look For
Dollar spot is favored by air temperatures ranging from 16–32°C (optimum 21–27°C) with extended periods of high humidity (>85% at night). The disease tends to be most severe under the following conditions: warm days, cool nights, infrequent rain but long dew periods, daily ground fogs that extend leaf wetness periods, and low nitrogen fertility. When the fungus is active and leaf surfaces remain wet, a fine, white, cobwebby mycelium covers the infection centers or diseased patches during early morning hours.
Symptoms of dollar spot can vary based on the turfgrass species and height of cut. Under close mowing heights, as with intensively maintained bentgrass or wintergrass, the disease appears as small circular strawcolored spots of blighted turf about the size of a 50 cent coin. On coarser textured turf maintained under higher mowing practices, such as Kentucky bluegrass or perennial ryegrass, the blighted areas are considerably larger, strawcolored patches 7.5–15 cm in diameter.
Affected patches frequently coalesce and involve large areas of turf. Grass blades generally die back from the tip with distinct hourglass shaped lesions that are strawcolored or bleached white. Hourglass bands may not appear on warm-season grasses.
Implementing proper cultural practices is crucial to reducing disease severity. Management tactics include: maintaining adequate nitrogen when dollar spot is active, making light frequent nitrogen applications, avoiding drought stress, limiting irrigation toward dusk, removing dew by mowing, poling, or rolling; aerifying to reduce compaction and thatch, and removing trees or adding fans to increase air circulation.
Fungicides are also important to manage dollar spot. Since dollar spot is a foliar disease, select spray nozzles and spray volumes that provide good coverage to maximize fungicide activity. Bayfidan and Dedicate are ideal for early season dollar spot control. Routine fungicide applications are commonly needed when air temperatures are 21–32°C; Rovral GT and 3sixty5 are especially helpful in hot weather since they are non-DMI’s and can be used without risk of negative plant growth effects. Extended periods of temperatures above 32°C may significantly slow dollar spot development.
Dollar spot resistance to certain classes of fungicides can be significant. Preventive applications and rotating fungicide classes, including the use of multi-site fungicides, is important for reducing the risk of resistance. Non-DMI’s like Rovral GT and 3sixty5 will control DMI-resistant dollar spot.