Dollar spot

Dollar spot is a destructive fungal disease affecting turfgrass, caused by the fungus Clarireedia bennettii (formerly Sclerotinia homoeocarpa). This pathogen is notorious for creating unsightly, straw-colored lesions that disrupt the uniformity of lawns, golf courses, and athletic fields, significantly reducing the visual quality of the grass.

The disease primarily targets a wide range of cool-season and warm-season grasses. Susceptible hosts include creeping bentgrass, Kentucky bluegrass, fescues, and perennial ryegrass. Turfgrass maintained under low nitrogen fertility levels or moisture-stressed conditions is particularly susceptible to infection, as these factors compromise the plant's natural defense mechanisms.

The primary symptom is the development of small, circular, silver or straw-colored spots roughly the size of a dollar coin. In the early morning, especially under high humidity, a fine, cottony white mycelium may be visible across the affected patches. If the disease remains unchecked, the spots can coalesce, leading to large, irregular areas of blighted, dead turf that require extensive repair.

The environmental conditions favoring the development of Clarireedia bennettii include prolonged periods of high humidity, moderate temperatures (60°F to 85°F), and the presence of dew on leaf blades. The fungus survives in thatch and soil, spreading through mycelial growth or windborne spores. Frequent rainfall or heavy irrigation followed by dry periods often creates the ideal microclimate for a flare-up.

Effective management requires an integrated approach. Cultural practices such as regular core aeration, promoting air circulation, and maintaining an adequate nitrogen fertilization program are critical for prevention. In severe cases, the use of chemical control is necessary, involving the application of registered systemic fungicides. Monitoring the lawn consistently ensures that early outbreaks are contained before they cause widespread damage.