Lawn fungus often manifests as unsightly patches or discoloration. These issues are typically a response to environmental factors that create a hospitable environment for fungal spores. Effective management requires addressing both the immediate symptoms and the underlying environmental conditions fueling the infection. The “disease triangle” requires a susceptible host (your lawn), the presence of a pathogen (the fungus), and a favorable environment, usually involving excessive moisture and specific temperatures.
Identifying Common Lawn Fungal Diseases
Accurate identification is the first step in effective treatment, as different fungi thrive under different conditions. Brown Patch is one of the most common diseases, appearing as circular or irregular patches of brown grass, typically 4 to 12 inches in diameter. These patches often exhibit a grayish border, sometimes called a “smoke ring,” and the fungus flourishes during periods of high heat and humidity.
Dollar Spot is another prevalent issue, named for the small, sunken, straw-colored spots it creates, which are roughly the size of a silver dollar, or 2 to 6 inches wide. The individual spots often display a tan lesion on the grass blade with a distinct reddish-brown border. These spots may eventually merge to form larger, irregular areas. Dollar Spot is frequently associated with inadequate nitrogen levels in the soil.
Red Thread is identifiable by the pink or red thread-like structures, called sclerotia, visible on the grass blades, especially when wet. The disease presents as tan or bleached-white circular patches up to two feet wide. This fungus prefers prolonged periods of cool, wet weather, making it more common during the spring and fall when turf growth is slowed.
Applying Fungicides for Immediate Control
Fungicides offer a direct way to stop the spread of an active infection or provide a protective barrier. These chemical treatments are categorized based on how they interact with the grass plant. Contact fungicides remain on the surface of the grass blades, acting as a shield to prevent fungal spores from penetrating the tissue. Since they do not enter the plant, they can be washed away by rain or irrigation and require reapplication as the grass grows.
Systemic fungicides are absorbed into the plant and move throughout its vascular system, treating the infection from the inside out. This type is useful for actively infected turf because it reaches the sites where the fungus is established. Systemic products provide longer-lasting protection and may be applied less frequently than contact formulas.
To treat an existing problem, a curative approach using a systemic fungicide is recommended at the first sign of disease. Preventive applications, typically using a contact product, should be timed before high-risk seasons, such as warm, humid summer months. Always apply these products early in the morning or late afternoon. Follow the label instructions precisely for mixing ratios and coverage to ensure the best results and reduce the risk of resistance.
Long-Term Cultural Practices to Prevent Recurrence
The most lasting solution for managing lawn fungus involves modifying the environment to make it less favorable for pathogens. Watering practices are a primary factor, as excessive moisture allows fungal spores to germinate and infect the grass. It is best to water deeply but infrequently, applying enough water to reach the root zone, rather than shallowly wetting the surface daily.
The time of day for irrigation is equally significant. Watering should be completed in the early morning hours, allowing the sun and air movement to dry the grass blades quickly. Fungi, especially foliar diseases, require many hours of continuous leaf wetness to successfully penetrate the plant. Avoiding late afternoon or evening watering is essential because the grass will remain wet overnight, creating optimal conditions for fungal growth.
Proper mowing height reduces stress on the grass, making it more resilient to disease. Never remove more than one-third of the grass blade height in a single mowing session, as this sudden reduction stresses the plant. Additionally, cleaning mower blades after use prevents the mechanical transfer of fungal spores from infected areas to healthy ones.
Balanced soil nutrition plays a substantial role in reducing fungal susceptibility. Applying too much nitrogen, especially in a fast-release form, can promote the succulent growth favored by diseases like Brown Patch. Conversely, a nitrogen deficiency makes the turf more vulnerable to Dollar Spot and Red Thread. Soil testing helps determine the precise nutrient needs to maintain a healthy, dense turf that resists pathogens.
Increasing air circulation and reducing soil compaction discourage fungal development. Aeration, which involves removing small cores of soil, improves the movement of air, water, and nutrients to the roots. Aeration also helps break down the thatch layer. Thatch, a layer of organic matter that accumulates on the soil surface, traps moisture and acts as a reservoir for fungal spores. Pruning nearby trees and shrubs that cast dense shade will increase sunlight and airflow, helping to dry the turf surface.