Damage from lawn disease on grass blades

How to Identify Lawn Disease & Treat Grass Fungus

Learn how to identify and treat lawn diseases with our expert guide on lawn diseases. Explore effective grass fungus treatments to keep your lawn healthy.

What causes lawn disease?

Lawn diseases can be alarming. They can cause thinning, damage your lawn, and, in most severe cases, kill grass. Most of the time, lawn diseases don’t cause much direct damage and are mostly cosmetic.

Fungi are the main culprits for diseases in home lawns, but just because a fungus is present doesn’t necessarily mean lawn disease will become an issue.

Enter: The disease triangle

The disease triangle: lawn disease requires a virulent pathogen (fungus), a susceptible host (grass that fungus can infect), and a favorable environment, all present at once. Favorable environmental conditions include extended leaf wetness, heavy nitrogen, and low mowing height. Removing any one factor — for example shortening leaf wetness duration, balancing nitrogen timing, or raising mowing height — makes disease far less likely even with the pathogen and host still present.

A pathogen (fungus), a susceptible host, and a favorable environment — measured by things like leaf wetness duration, nitrogen timing, and mowing height — all have to align for lawn disease to take hold.

How to identify lawn diseases

Lawn disease identification table. Fairy ring shows circular rings of mushrooms. Necrotic ring spot shows straw-colored rings, often with healthy grass in the center, which can resemble pet patches. Summer patch shows circular patches of yellow or brown grass, often with orange or brown edges. Anthracnose shows yellow or bronze patches of wilted turf. Brown patch shows irregular 4-inch or larger patches of brown or yellow grass. Dollar spot shows 1-6 inch straw-colored patches with white or tan leaf lesions edged in reddish-brown. Gray leaf spot shows gray, olive, or brown leaf lesions with a darker brown border. Pink or gray snow mold shows grayish to pink, matted patches. Pythium blight shows reddish-brown, slimy or cobwebby spots. Red thread shows pink to red patches with reddish hairs or threads on individual grass leaves. Rust shows yellow or rust-colored powder on shoes, mowers, and grass leaves, and is typically cosmetic without significant grass damage.

Learn more about: Fairy ring, Necrotic ring spot, Summer patch, Anthracnose, Brown patch, Dollar spot, Gray leaf spot, snow mold, Pythium blight, Red thread, Rust

Getting rid of lawn disease

Most lawns can withstand some disease pressure without the need for fungicides. When you do notice disease issues and want to avoid fungicide applications, these 3 steps can help get rid of disease:

Audit your irrigation system to ensure you’re watering properly
Reduce other lawn stressors:
1. Repair traffic
2. Reduce shade
Sharpen your mower blades to ensure a clean cut

If you face the same disease issues season after season, consider switching to a more resistant grass cultivar or species.

Prevent lawn disease

We know it can be tempting to reach for the fungicides to help prevent—or treat—disease issues. But at Sunday, we try to limit harsh pesticide use and opt in for a more integrated pest management approach to lawn diseases, focusing on prevention in an effort to avoid disease issues (and fungicide use) in the first place.

Without preventative fungicide use, disease prevention should focus on the other two corners of the disease triangle: either changing the grass, or changing the environment.

Grass selection. Some grasses are just naturally vulnerable to certain diseases, and resistant to others. Select high-quality, disease-resistant grasses suitable to your region to help prevent disease issues.
Watering. Incorrect watering practices are one of the main issues leading to ideal environmental conditions for fungal growth. Wet leaves create the perfect conditions for the spread and growth of many fungal diseases. Water early in the morning to allow leaves time to dry off during the day, and water deeply and infrequently to build strong, healthy turf that is more resilient against disease.
Fertilizing. A well-fed turf is a more disease-resistant turf. With too little nutrition, your grass might be too weak to fight off infection, but too much fertilizer can cause succulent growth that promotes some diseases.
Mowing. Dull blades shred the grass, weakening the turf and opening the grass up to infection—while mowing too low can further stress the grass. Sharpen your mower blades regularly so you get a clean cut, mow at the right height for your grass type, and remove clippings if you have visible disease present, to avoid spreading fungal spores across the lawn.
Stress. Stressed grass is susceptible grass. Address issues like compaction, shade, and traffic to reduce stress on your grass and help it withstand a little disease pressure.

Cited sources

Turf: Disease Management for Home Lawns. University of Massachusetts Amherst Extension.

Turfgrass Disease Control. University of Missouri Extension.

Turfgrass Diseases: Quick Reference Guide. University of Georgia Extension.

Photo credit: Donald Groth, Louisiana State University AgCenter, Bugwood.org

Lawn Lawn Disease Identification Lawn Repair Lawn Help Guide

Paige Boyle

Updated on September 17, 2026

Paige received her B.S. in Environmental, Soil, and Water Sciences with minors in Horticulture and Wildlife Management and her M.S. in Horticulture with an emphasis on Turfgrass Management from the University of Arkansas, and is currently a PhD Candidate at Utah State University, where she studies turfgrass ecology. Her background includes vermicomposting, earthworm ecology, compost processing, recycling and waste management, and stream restoration design.