Turfgrass fungus is a pathogen that attacks the grass blades and roots, leading to unsightly patches and weakening the entire lawn structure. Fungal organisms require specific conditions, often heat and humidity, to reproduce and spread across a yard. Managing these environmental triggers is the first step toward effective eradication and long-term prevention. This guide offers practical methods for identifying, treating, and preventing fungal diseases in your lawn.
Recognizing Common Lawn Fungal Diseases
One of the most common issues is Dollar Spot, which appears as small, bleached circular patches approximately the size of a silver dollar. These spots may merge into larger irregular areas and often feature lesions on the grass blades that are tan with a reddish-brown border.
Brown Patch, caused by the Rhizoctonia solani fungus, thrives in warm, humid weather. This disease creates large, irregularly shaped rings or circular areas of thinned, brown turf that can range from a few inches to several feet in diameter. In the early morning, a grayish-purple border, sometimes called a smoke ring, may be visible around the patch’s edge, particularly on shorter-cut lawns.
Slime Mold often presents as a dusty, gray, white, or yellowish residue coating the grass blades. While these organisms do not infect the grass plant itself, their presence can shade the turf, limiting photosynthesis. Slime mold appears during periods of prolonged high humidity and is primarily a cosmetic concern.
Immediate Non-Chemical Control Methods
Adjusting the watering schedule is the most impactful change, as it reduces leaf wetness duration, a primary requirement for most fungal growth. Watering deeply and infrequently, such as one inch of water once or twice a week, encourages deeper root growth and allows the soil surface to dry out.
Water only in the early morning, ideally between 4 a.m. and 10 a.m., so the sun and air circulation can quickly evaporate moisture from the grass blades. Watering in the late afternoon or evening leaves the turf wet throughout the night, creating perfect conditions for fungal development.
Dethatching removes the thick layer of dead and living organic matter (thatch) that accumulates between the soil and the grass blades. A thatch layer thicker than three-quarters of an inch acts as a sponge, retaining moisture and harboring fungal pathogens.
Aeration pulls small plugs of soil from the ground, immediately improving air circulation and water penetration into the root zone. This process relieves soil compaction, allowing the root system to breathe and promoting the decomposition of excess thatch. Increasing oxygen levels in the soil creates an environment less favorable for fungi that prefer stagnant, waterlogged conditions.
Choosing and Applying Fungicides
When cultural practices alone do not stop a severe outbreak, chemical controls become necessary to eradicate the pathogen. Fungicides are classified as either contact or systemic, each with a different mode of action against the fungus. Contact fungicides form a protective barrier on the surface of the grass blade, killing fungal spores upon contact and providing quick, curative action.
Contact products do not penetrate the plant tissue and must be applied frequently, as mowing or new growth removes the protective layer. Systemic fungicides are absorbed by the grass roots or leaves and move throughout the plant’s vascular system, providing long-lasting protection. They treat existing infections within the plant tissue, offering both curative and preventative benefits.
For the most effective treatment, alternate between different chemical classes to prevent the fungus from developing resistance. A curative application may require two to three treatments, spaced seven to fourteen days apart, depending on the product label instructions. When applying any chemical, wear appropriate personal protective equipment and ensure the product is applied evenly using a properly calibrated spreader or sprayer.
Long-Term Strategies for a Fungal-Resistant Lawn
Maintaining turfgrass health is the most effective long-term defense against future fungal outbreaks. Adjusting the mowing height to the upper end of the recommended range for your grass species is a key preventative measure. Taller grass blades develop a deeper, more robust root system, helping the plant better withstand environmental stresses, including disease pressure.
Follow the “one-third rule,” meaning you should never remove more than one-third of the grass blade height in a single mowing session. Excessive removal stresses the plant, making it more susceptible to pathogen infection. Returning grass clippings to the lawn can also recycle nutrients, provided the turf is not actively diseased.
Balanced nutrition, specifically managing nitrogen application, is crucial. Over-fertilizing with quick-release nitrogen causes excessive, tender growth vulnerable to fungal attack, such as Brown Patch. Utilizing slow-release nitrogen sources and ensuring adequate potassium levels promotes strong, disease-resistant cell walls.
Conducting a soil test every few years provides data on soil pH and nutrient deficiencies. Correcting highly acidic or alkaline soil pH, typically by adding lime or sulfur, helps the grass roots efficiently absorb necessary nutrients. A nutrient-rich, pH-balanced soil environment supports dense, resilient turf that naturally resists fungal proliferation.