Dollar spot is a widespread fungal disease of turfgrass caused by the pathogen Clarireedia homoeocarpa. This common affliction affects nearly all lawn types, including creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. The disease attacks the leaf tissue, leading to aesthetic damage and a decline in lawn quality. Understanding the distinct symptoms and environmental triggers is the first step toward effective management.
Identifying Dollar Spot
The disease is named for the characteristic symptoms it produces on closely mown turf: small, circular, sunken spots typically one to two inches in diameter. On taller turf, such as residential lawns, these spots may expand up to six inches or more. The affected areas appear bleached white or straw-colored, often merging to create large, irregular patches of blighted turf.
Closer examination of individual grass blades reveals distinct lesions with a unique hourglass shape. These lesions are usually light tan in the center, bordered by a reddish-brown margin, and they can girdle the leaf blade, causing the tip to die back. In the early morning, a short, fuzzy, white fungal growth, known as mycelium, may be visible within the affected spots, especially when dew is present.
Conditions Favoring Disease Development
The pathogen becomes active across a broad temperature range, typically between 60°F and 85°F. The most significant factor for infection is the duration of leaf wetness, which must be continuous for approximately 10 to 12 hours. This wetness is often supplied by heavy morning dews, frequent rain, or improper irrigation practices.
Turfgrass suffering from a deficiency in nitrogen fertility is considerably more susceptible to infection and recovers slowly. Other factors that encourage disease development include excessive thatch accumulation, which holds moisture near the leaf surface, and low air movement.
Cultural Management Strategies
Modifying cultural practices creates an environment less favorable for the fungus. A robust fertilization program is necessary, as maintaining adequate nitrogen levels helps the turf outgrow the lesions and accelerates recovery. Light, frequent applications of nitrogen are recommended to sustain moderate, consistent growth throughout the season, rather than applying large amounts infrequently.
Adjusting irrigation is equally important to reduce the duration of leaf wetness. Watering should be deep and infrequent, supplying moisture to the root zone while allowing the surface to dry out. The most suitable time for irrigation is early morning, generally between midnight and 6 AM, which minimizes the period the leaves remain wet.
Actively removing morning dew is another effective tactic. This can be accomplished by lightly dragging a hose, a rope, or a specialized dew whip across the lawn surface, or by mowing the turf in the morning to disrupt the dew layer. Core aeration and vertical mowing can reduce excess thatch, improving air circulation and surface drainage, which limits the disease’s ability to establish.
When to Consider Fungicides
While cultural practices resolve most cases, chemical control may be necessary for severe, recurring outbreaks or for turf requiring a higher aesthetic quality. Fungicides are most effective when applied preventatively, before the disease becomes widespread, or at the first sign of symptom development.
Two main types of products are used: contact fungicides, which remain on the leaf surface, and systemic fungicides, which are absorbed by the plant. Because the dollar spot pathogen has a high potential to develop resistance, a resistance management strategy is necessary. This involves rotating between different classes of fungicides after each application, ensuring the active ingredients have different modes of action for sustained control.