Dollar spot is a common fungal disease that affects high-quality turfgrass, causing widespread damage on golf courses, athletic fields, and home lawns. It affects nearly all turfgrass species, though it is particularly noticeable in closely mown grasses like creeping bentgrass and annual bluegrass. Understanding the visual signs, the conditions that promote its growth, and effective control methods is necessary for managing this persistent problem.
Visual Identification of the Disease
The disease earns its name from the appearance of small, circular, sunken patches of dead grass on closely mown turf. These spots typically measure one to three inches in diameter and are initially bleached or straw-colored. On turf mown at taller heights, the spots may reach six inches across and can merge to form large, irregular areas of blighted grass.
The most specific symptom occurs on the individual grass blades, which develop distinct lesions. These lesions are usually tan with a dark reddish-brown border and often exhibit an hourglass shape, wider at the edges and narrow in the center. This hourglass pattern helps differentiate dollar spot from other turf diseases.
During active disease growth, typically in the early morning when heavy dew is present, a fine, white, cobweb-like fungal growth (mycelium) may be visible across the affected spots. The causal fungus, Clarireedia jacksonii, survives unfavorable conditions, such as winter, as pseudosclerotia (a thick-walled crust of mycelium) in the thatch and on infected plant debris.
Environmental Triggers and Causal Agent
The fungal pathogen responsible for dollar spot is Clarireedia jacksonii. This fungus is highly dependent on specific environmental conditions to initiate infection. The disease is most active when air temperatures are moderate, ranging from 60°F to 85°F, combined with high humidity levels.
Prolonged periods of leaf wetness are a primary trigger, often occurring when dew remains on the grass blades for eight hours or more. This extended moisture allows the fungus to penetrate the leaf tissue and spread. The disease can occur anytime from spring through fall, peaking in late summer or early fall when warm days are followed by cool nights and heavy dew.
Low soil nitrogen is a significant contributing factor, limiting the turfgrass’s ability to grow new tissue and recover. Nitrogen-deficient turf is more susceptible to outbreaks. Drought stress and excessive thatch accumulation also encourage disease development.
Effective Management and Prevention Techniques
Controlling dollar spot relies heavily on cultural practices that reduce leaf wetness and promote healthy turf growth. Watering should be done deeply and infrequently, preferably in the early morning. Early morning irrigation washes the dew off the leaves and allows the grass to dry completely before nightfall, minimizing leaf wetness duration.
Removing morning dew through physical means is another effective control method. This can be accomplished by mowing, lightly dragging the surface with a weighted hose or pole, or using a lightweight roller. Improving air circulation by pruning nearby trees or shrubs also helps the grass canopy dry faster.
Maintaining adequate nitrogen fertility is important for both prevention and recovery. Small, frequent applications of nitrogen fertilizer are recommended to promote steady growth without causing excessive growth surges. This ensures the grass can continuously grow out of the spots caused by the fungal infection.
For severe or persistent outbreaks, chemical control with fungicides may be necessary. Preventative applications, timed before the disease appears, are more effective than curative treatments. Homeowners should consult local extension services for specific product recommendations and application timing, as the fungus can develop resistance over time.