Dollar spot

This pathogen does not produce survival structures known as sclerotia but survives as mycelium within infected plant debris and the thatch layer. It thrives in various turf species, including creeping bentgrass, Kentucky bluegrass, and ryegrass.

Transmission occurs through the movement of infected clippings, equipment, shoes, or water. Once introduced, the mycelium rapidly infects the leaves of susceptible grasses by entering through stomata or wounds.

The fungus is highly aggressive in specific environmental conditions. It spreads across the lawn surface, creating new infection points as it colonizes the leaf blades and breaks down plant tissue.

The persistence of the pathogen in the thatch ensures that the disease can reappear annually if environmental triggers are met and if the turf's resistance remains low due to poor maintenance.

The hallmark symptom is the appearance of small, circular, sunken spots on the turf, typically 1 to 2 inches (2–5 cm) in diameter, resembling silver dollars on close-cut turf.

Initially, affected leaves show water-soaked lesions that turn chlorotic (yellow) and then bleach to a straw or tan color. On larger-mown turf, the spots may be larger and less distinct.

Under high humidity and cool mornings, a fine, white, cottony mycelium can be observed on the infected patches, which quickly disappears as the dew evaporates and sunlight increases.

As the disease progresses, individual patches can coalesce into large, irregular, blighted areas, leading to extensive damage and a significant reduction in the quality and uniformity of the lawn.

• Circular straw-colored spots on turf.
• Water-soaked lesions on individual blades.
• White, cobweb-like mycelium seen in the morning.
• Reddish-brown border often present on the spots.
• Dieback of the turfgrass in severely affected areas.

Dollar spot development is favored by temperatures ranging from 60°F to 85°F (15°C–30°C). Warm days and cool nights with heavy dew are especially conducive to its rapid spread.

Extended periods of leaf wetness are critical for the infection process. High relative humidity and poor air circulation significantly exacerbate the development of the fungal mycelium.

Low nitrogen fertility levels are a primary driver of disease severity. Grass suffering from nutrient deficiency is significantly more susceptible to infection by Clarireedia species.

Drought-stressed turf is often more prone to damage. When grass is under water stress, it cannot grow rapidly enough to outpace the fungal infection, leading to more visible scarring.

Excessive thatch buildup and poor drainage contribute to the disease by keeping the surface moist for longer periods, providing the perfect microclimate for the pathogen to thrive.

The primary harm is the destruction of the turf's aesthetic appeal, making it unsuitable for high-quality lawns, golf greens, or sports fields due to the permanent spotting effect.

In severe cases, the fungus causes systemic damage, leading to crown death and thin, sparse turf. This leaves the lawn vulnerable to weed infestation and requires expensive renovation.

Infected turfgrass becomes weakened and less resilient to other stresses, such as high traffic, heat, or cold, which can lead to rapid turf loss on high-use areas.

For professional turf managers, dollar spot requires intensive monitoring and costly fungicide programs to maintain the high standards required for competitive play or public display.

The economic impact is substantial, involving not only the cost of chemical control but also the long-term expense of restoring dead patches and overseeding damaged zones.

Maintaining adequate nitrogen levels is essential for prevention. A consistent fertilization program ensures the grass remains vigorous and can quickly recover from minor infections.

Irrigate early in the morning to minimize the duration of leaf wetness. This allows the blades to dry off during the day, significantly reducing the window of opportunity for fungal infection.

Cultural practices like aeration and vertical mowing are vital to increase air circulation, reduce surface humidity, and remove excess thatch where the pathogen survives.

When the disease reaches a threshold, apply appropriate fungicides. It is recommended to rotate chemical classes (FRAC codes) to prevent the development of resistant fungal strains.

Clean all maintenance equipment thoroughly before moving from infected areas to healthy parts of the lawn to prevent the mechanical spread of the fungus.