Gardening Caring for Your Yard Lawn Care 12 Most Common Lawn Diseases and How to Prevent Them One of these common lawn diseases might be at work if your turf is marked by dead spots and discoloring. By Megan Hughes Megan Hughes Megan Hughes has a passion for plants that drives her to stay on top of the latest garden advancements and time-tested ways of growing great plants. She travels regularly to learn about new plants and technology and is closely connected to the innovation side of the horticulture industry. She has more than 25 years of experience in horticulture. Learn about BHG's Editorial Process Published on September 10, 2024 Close Photo: Marty Baldwin Even well maintained grass can sometimes be plagued with a lawn disease. When the just-right combination of pathogens, environmental factors, and susceptible grass coincide, plant diseases can gain a foothold. The first step in combatting the problem is identifying the specific disease infecting your turf. This quick reference guide highlights the 12 most common lawn diseases and provides ways to cure and prevent them. 01 of 12 Brown Patch Singjai20 / Getty Images As its name implies, brown patch disease forms circular patches of dead grass that measure a few inches to a few feet across. Most grass species turn brown when infected with brown patch, but St. Augustinegrass takes on a straw-colored hue. Brown patch is most prevalent in hot, humid weather when the soil is saturated. When: Spring, summer, and fall during times of high humidity and wet soil Susceptible grasses: All turfgrasses What to do: Irrigate deeply and infrequently, allowing the soil to dry slightly between waterings. Don’t overfertilize. Too much nitrogen fertilizer encourages the growth of brown patch. Don’t fertilize when the disease is active. How Often—and How Long—You Should Water Your Grass 02 of 12 Dollar Spot nycshooter / Getty Images Known for causing circular straw-colored patches of turf a few inches across, dollar spot often multiplies, and the spots merge to form irregular patches, mimicking summer patch disease. Where the infection is aggressive, white fungus growth is easy to spot on infected plants in the early morning. When: Summer during high humidity and dry soil conditions Susceptible grasses: All turfgrasses What to do: Water deeply and infrequently in the morning to minimize the time leaf blades are moist. Fertilize with nitrogen to boost plant growth. 03 of 12 Fairy Rings beekeepx / Getty Images Fairy rings often appear seemingly overnight. Most well-known for forming a circle or arc of white mushrooms, some fairy rings don’t include mushrooms but simply a ring or arc of lush, dark green grass. Some fairy rings include a band of dead grass. No matter which type of fairy ring you are dealing with, the ring or arc shape is present and points to the underground fungal cause of the unique lawn phenomenon. When: Warm, wet weather in summer and fall Susceptible grasses: All turfgrasses What to do: Aerate the lawn to remedy soil compaction and encourage strong plant growth. Lightly fertilize as determined by a soil test. 04 of 12 Gray Leaf Spot Praewpailin / Getty Images Gray leaf spot begins as small, brown spots on grass leaves and stems. With spore production, the spots enlarge and become blue-gray and fuzzy. Dead spots of turf often grow together to form irregular dead patches. When: Summer during times of high humidity Susceptible grasses: Many grasses are susceptible, but gray leaf spot is especially common in St. Augustinegrass and perennial ryegrass lawns. What to do: Manage irrigation well to control gray leaf spot. Water deeply and infrequently in the morning to minimize the time leaf blades are wet. Also, mow regularly to remove excess leaf tissue and encourage good airflow through the turf. 05 of 12 Helminthosporium Leaf Spot Tomasz Klejdysz / Getty Images Take a close look at leaf blades to check for Helminthosporium leaf spot. This fungal disease produces small dark spots or streaks on leaf blades. The spots are more numerous near the base of the leaf. A lawn infected with Helminthosporium leaf spot will become brown and thin. When: Spring, summer, and fall during long periods of wet weather. Susceptible grasses: Perennial ryegrass, tall fescue, and all warm-season grasses What to do: Irrigate the lawn deeply and as infrequently as possible. Take a soil test to check nutrient levels. Fertilize as necessary. Aerate to promote strong root growth. The 6 Best Lawn Aerators for a Stunning Yard 06 of 12 Necrotic Ring Spot photo_Pawel / Getty Images Cool, wet growing conditions followed by heat and drought are favorable for necrotic ring spot to flourish. Most common on newly sodded lawns with compacted soil, necrotic ring spot forms circular, straw-colored patches less than 12 inches in diameter. Often, grass regrows in the center of the patch, creating a “frog-eye” appearance with green grass circled by a ring of dead turf. When: Spring, summer, fall Susceptible grass: Kentucky bluegrass What to do: Aerate soil to remedy soil compaction and encourage strong plant growth. If poor drainage is prevalent, improve water movement through the soil profile of the lawn. Fertilize turf that is nutrient deficient. 07 of 12 Pythium Blight Denny Schrock Pythium blight appears when the soil is saturated from over-irrigation or repeated rounds of heavy rain showers. At first, small, irregular dark spots appear on the turf, and then the grass dies rapidly, leaving behind matted dead spots. When: Year-round during times of excessive moisture Susceptible grasses: Warm-season grasses, including bermudagrass, centipedegrass, and St. Augustinegrass What to do: If over-irrigation is the culprit, correct the watering schedule. Improve turf drainage through aeration and topography to help your lawn shed water well after heavy rains. 08 of 12 Red Thread Tomasz Klejdysz / Getty Images True to its common name, red thread disease forms thread-like filaments on infected grass blades. At first glance, the irregular beige-to-brown dead patches resemble many other grass diseases, but close inspection reveals the tiny threads. When: Spring through fall in wet, cool conditions Susceptible grasses: Kentucky bluegrass, perennial ryegrass, fine fescues What to do: When the disease is active, collect clippings to discourage spread. Provide adequate nitrogen fertilizer. 09 of 12 Rust Dean Schoeppner Rust is easy to identify. Simply look at your shoes after walking across rust-infected turf. Your shoes will take on a red-brown cast from rust’s fungal spores. While rust discolors clothing and equipment, it often disappears as soon as weather conditions change. When: Summer and fall in high humidity and shade Susceptible grasses: Kentucky bluegrass, perennial ryegrass, bentgrass, zoysiagrass, bermudagrass, and fescue What to do: Discourage persistent rust by pruning trees and other plants to maximize light and airflow for your lawn. 10 of 12 Slime Mold Denny Schrock Prolonged moist growing conditions can spur slime mold to form on grass blades. The black, blue-gray, yellow, tan, or white fungi grow on leaf blades, limiting the plant’s ability to photosynthesize. During extended periods of wet, rainy weather, the grass may become thin and weak due to its inability to manufacture nutrients, but slime mold is rarely deadly to the plant. When: Year-round during wet, rainy weather Susceptible grasses: All turfgrasses What to do: Remove slime mold by mowing. Rake and dispose of clippings. Warm, dry weather quickly eliminates slime mold. 11 of 12 Snow Mold Tunatura / Getty Images This group of diseases is prevalent in cold regions with prolonged snow cover. Snow mold diseases (pink snow mold, gray snow mold) are characterized by circular gray- or straw-colored patches of lawn grass ranging from a few inches in diameter to more than a foot. The patches are often noticed shortly after snow melts in spring. When: Early to late spring Susceptible grasses: Kentucky bluegrass, tall fescue, perennial ryegrass What to do: Rake and lightly fertilize damaged areas in spring to encourage growth. Prevent snow molds by preparing the lawn well for winter. Remove or mulch leaf litter and mow regularly until the grass goes into dormancy in late fall. The 9 Best Organic Lawn Fertilizers 12 of 12 Summer Patch Bilal photos / Getty Images When 3- to 5-inch-wide wilted spots of turf appear in a lawn during the heat of the growing season, summer patch might be at work. This lawn disease often consists of several spots that merge to form irregular dead patches. When: Summer and hot, moist conditions Susceptible grasses: Kentucky bluegrass and fine fescues What to do: Water deeply and infrequently during dry periods to minimize the time leaf blades are moist. Aerate to reduce soil compaction and promote strong plant growth. Was this page helpful? Thanks for your feedback! Tell us why! Other Submit