Dollar spot is a common turfgrass disease that impacts lawns, sports fields, and golf courses across the globe. This fungal disease is caused by pathogens in the genus Clarireedia, which were previously classified under Sclerotinia. Understanding the appearance of this disease and the conditions that favor its development is the first step toward effective management and control.
Visual Symptoms and Identification
The most recognizable sign of the disease is the appearance of small, circular, sunken patches of dead grass. On closely mown turf, these spots are typically white or tan and approximately one to two inches in diameter, which is how the disease earned its common name. In home lawns, the spots may be larger, reaching two to five inches across, and can merge to form large, irregular areas of blighted turf.
A closer look at individual grass blades reveals more specific diagnostic symptoms. The leaves often develop light tan lesions bordered by a reddish-brown or dark-brown band. These lesions frequently appear in a distinctive hourglass or “dog-bone” shape that girdles the leaf blade. In the early morning, white, cobweb-like fungal threads, known as mycelium, may be visible stretching across the affected leaves.
Conditions Driving Fungal Growth
The fungus requires specific conditions to become active and cause disease. This pathogen thrives during periods of warm days and cool nights, particularly when temperatures are between 59°F and 86°F. High humidity combined with prolonged leaf wetness is a major factor that encourages the disease to flourish.
Leaf wetness, caused by dew, rain, or poor irrigation, provides the necessary moisture for the fungus to infect the grass. Turfgrass stressed by a deficiency in nutrients, especially nitrogen, is significantly more susceptible to outbreaks. Low nitrogen levels prevent the turf from outgrowing the damage caused by the foliar-attacking fungus.
Non-Chemical Control Strategies
Managing dollar spot relies heavily on cultural practices that create an environment less favorable for the fungus. Optimizing soil fertility is key, specifically by ensuring adequate nitrogen levels throughout the growing season. Light and frequent applications of nitrogen fertilizer stimulate new leaf growth, allowing the turf to recover from the disease spots.
Controlling leaf wetness is another important strategy achieved through several methods:
- Watering deeply and infrequently, preferably between midnight and 6:00 a.m., allows the foliage to dry completely during the day.
- Improving air circulation by pruning trees and shrubs helps the grass canopy dry more quickly.
- Removing excessive thatch accumulation aids in drying.
- Physically removing dew in the morning by lightly dragging a hose or rope across the turf, or by mowing, shortens the leaf wetness period.
Using Fungicides for Severe Outbreaks
For turf areas that experience severe or persistent dollar spot, chemical intervention with fungicides may be necessary to suppress the disease. Fungicide applications are most effective when used preventatively, applied before symptoms are visible and environmental conditions are favorable for an outbreak. Once the disease is widespread, a curative application may be required, often using higher rates and shorter intervals between treatments.
The fungus can quickly develop resistance to certain chemical classes, requiring a resistance management strategy. This involves rotating between different types of fungicides or tank-mixing products with multiple modes of action to maintain efficacy. Homeowners should consider hiring a professional lawn service, as they have access to a broader range of products and the expertise for proper application.