Lawn diseases are infections of turfgrass, almost all of them caused by fungi. A disease develops only when a pathogen, a susceptible grass and a favorable environment are present at the same time, a relationship known as the disease triangle; removing any one of the three prevents it. Watering mistakes, fertilizer or mowing errors, compaction and chemical damage can all produce symptoms that look like disease.[1]
Brown patch and large patch
Different strains of the fungus Rhizoctonia solani cause both diseases. Brown patch affects cool-season grasses such as tall fescue, ryegrass and bluegrass and can kill young tall fescue; large patch affects warm-season grasses, mainly centipedegrass, zoysiagrass and St. Augustinegrass. Both appear as roughly circular brown patches from a few inches to several feet across.[2] In Georgia, brown patch usually appears in April and can stay active through October, favored by humidity, nights of 65 °F or warmer and days above 80 °F, while large patch is triggered by cooler nights of about 55 °F.[3]
Dollar spot
Dollar spot, caused by Sclerotinia homoeocarpa, is described by University of Missouri Extension as the most common turf disease worldwide; it affects nearly all grasses except tall fescue and is more severe on underfertilized turf.[4] In Georgia it is the most common spring lawn disease, forming sunken, straw-colored spots a few inches across.[3]
Pythium blight
Pythium blight can badly damage perennial ryegrass and annual bluegrass within two to three days, leaving leaves matted and greasy, sometimes with gray cottony growth. It is favored by nights above 65 °F with long periods of leaf wetness, and outbreaks often follow evening summer thunderstorms.[5]
Gray leaf spot
Gray leaf spot affects perennial ryegrass most severely, tall fescue to a lesser degree and St. Augustinegrass the least. It is favored by temperatures of 70–95 °F, at least 14 hours of leaf wetness and lush growth from heavy nitrogen.[6]
Spring dead spot
Spring dead spot is caused by soil fungi (Ophiosphaerella species) that rot bermudagrass roots, rhizomes and stolons. Bleached, dead patches from six inches to several feet across stand out when the lawn greens up in spring; infection is most active in moist fall weather, and cold, wet winters make it worse.[7] It affects only bermudagrass and recurs in the same spots unless managed.[3]
Diseases of northern lawns
Snow mold leaves straw-colored, matted patches as snow melts. Gray snow mold is caused by Typhula species and pink snow mold by Microdochium nivale; the main risk is long snow cover on unfrozen ground, and prevention includes avoiding heavy fall nitrogen and keeping thatch to half an inch or less.[8] Summer patch, caused by Magnaporthe poae, forms "frog-eye" patches, mainly in Kentucky bluegrass, and is made worse by heavy spring nitrogen and thatch.[9] Red thread, caused by Laetisaria fuciformis, forms pinkish-red patches with thread-like structures on bluegrass, ryegrass and fine fescue, and is favored by slow growth in cool, wet weather.[10]
Rust and fairy ring
Rust, caused by Puccinia fungi, produces orange spore pustules on grass blades that can stain shoes. Unlike most turf diseases it is most severe in drought and on slow-growing, stressed turf.[11] Fairy rings are caused by soil-dwelling fungi that do not infect roots; they appear as rings of mushrooms, dark-green grass or dead grass where the soil becomes water-repellent.[12]
Prevention and management
Cultural practices are the main defense. Watering deeply and infrequently in the early morning limits the hours that leaves stay wet; Clemson notes that brown patch spreads with more than ten hours of leaf wetness.[2][1] Other measures include avoiding excessive nitrogen, keeping thatch under half an inch, improving drainage and aerating during vigorous growth.[1][5] UC IPM notes that fungicides are rarely needed on well-chosen, well-maintained lawns; where they are used, Clemson advises alternating fungicide classes and following label directions.[1][2]
For an accurate diagnosis, UC IPM advises collecting whole plants with roots and soil from the edge of an affected area, keeping them cool and moist, and sending them to a plant disease diagnostic laboratory.[1] The University of Illinois Plant Clinic in Urbana is one such laboratory.[13]
References
- ^ ^ ^ ^ ^ Hartin; Geisel; Harivandi (September 2011). "Lawn Diseases: Prevention and Management" (Pest Notes 7497). UC Statewide Integrated Pest Management Program. ipm.ucanr.edu
- ^ ^ ^ "Brown Patch & Large Patch Diseases of Lawns" (HGIC 2150). Clemson Cooperative Extension Home & Garden Information Center, updated August 21, 2025. hgic.clemson.edu
- ^ ^ ^ Kolich, Heather (April 1, 2026). "Dead Circles in the Lawn and What to Do about Them". UGA Extension, Forsyth County. site.extension.uga.edu
- ^ "Dollar Spot". University of Missouri Extension, Turfgrass Science. extension.missouri.edu
- ^ ^ Butler; Kerns (revised December 16, 2019). "Pythium Blight in Turf". NC State Extension. content.ces.ncsu.edu
- ^ Butler; Kerns (revised December 16, 2019). "Gray Leaf Spot in Turf". NC State Extension. content.ces.ncsu.edu
- ^ Williamson, Joey (updated August 21, 2025). "Spring Dead Spot" (HGIC 2153). Clemson Cooperative Extension Home & Garden Information Center. hgic.clemson.edu
- ^ Engelbrecht, Christine (January 9, 2024). "Snow Mold". Iowa State University Extension and Outreach. yardandgarden.extension.iastate.edu
- ^ "Summer Patch". University of Missouri Extension, Turfgrass Science. extension.missouri.edu
- ^ Madeiras, Angela. "Red Thread on Lawns". UMass Amherst Center for Agriculture, Food, and the Environment. umass.edu
- ^ "Rust". University of Missouri Extension, Turfgrass Science. extension.missouri.edu
- ^ "Fairy Ring". University of Missouri Extension, Turfgrass Science. extension.missouri.edu
- ^ "Plant Clinic". University of Illinois Extension. extension.illinois.edu