As the name suggests, brown patch forms circular patches of dead grass, ranging from a few inches to several feet in diameter. Most turfgrasses turn brown when infected, while St. Augustinegrass appears straw-colored. Brown patch is most common in hot, humid weather when the soil is saturated.
Solution: Water deeply but infrequently, allowing the soil to dry slightly between waterings. Avoid excessive fertilization, especially nitrogen, which can promote the disease. Do not fertilize during active disease periods.
Susceptible grasses: All turfgrass types
Timing: Spring, summer, and fall during periods of high humidity and moist soil
2. Dollar Spot
Dollar spot causes small, round, straw-colored patches a few inches wide on the lawn. The fungus often spreads, and the spots can merge into irregular blotches, resembling summer patch. In heavily infected areas, white fungal growth can often be seen on affected grass in the early morning.
Timing: Summer with high humidity and dry soil
Susceptible grasses: All turfgrass types
Solution: Water thoroughly in the morning but avoid frequent watering to reduce leaf wetness duration. Apply nitrogen fertilizer to stimulate grass growth.
3. Fairy Rings
Fairy rings often seem to appear overnight. The most common type is a circle or arc of white mushrooms, but some fairy rings consist only of lush, dark green grass, and others may have a ring of dead grass. Regardless of the type, the circular or arched shape is a sign of underground fungi at work.
Timing: Warm, humid weather in summer and fall
Susceptible grasses: All turfgrass types
Solution: Aerate the lawn to reduce compaction and promote healthy growth. Fertilize based on soil test results.
4. Gray Leaf Spot
Gray leaf spot begins as small brown lesions on grass blades and stems. As spores develop, the spots expand and turn bluish-gray with indistinct margins. Dead patches on the lawn often coalesce into large, irregular areas.
Timing: High humidity during summer
Susceptible grasses: Especially common in St. Augustinegrass and perennial ryegrass, though many grasses can be affected
Solution: Manage irrigation carefully to control the disease. Water moderately in the morning, and avoid frequent watering. Mow regularly to remove excess foliage and improve air circulation.
5. Helminthosporium Leaf Spot
Check for small black spots or streaks on the leaves, especially near the base. This fungal disease, caused by Helminthosporium spp., can cause the lawn to thin and yellow.
Timing: Spring, summer, and fall during extended wet periods
Susceptible grasses: Perennial ryegrass, tall fescue, and all warm-season grasses
Solution: Water deeply but reduce watering frequency. Test soil for nutrient levels and fertilize accordingly. Keep soil aerated to support root growth.
6. Necrotic Ring Spot
Cool, damp growing conditions followed by hot, dry weather favor the development of necrotic ring spot. This disease is most common in newly sodded lawns with compacted soil. It forms circular, straw-colored patches less than 12 inches in diameter. Grass may regrow in the center, creating a “frog-eye” appearance.
Timing: Spring, summer, and fall
Susceptible grasses: Kentucky bluegrass
Solution: Aerate soil to reduce compaction and promote vigorous growth. Improve moisture movement in poorly draining areas. Fertilize lawns that are nutrient-deficient.
7. Pythium Blight
Pythium blight occurs when soil becomes saturated due to excessive irrigation or prolonged heavy rain. Initially, small irregular dark patches appear on the lawn, then grass quickly dies, leaving matted patches.
Timing: Wet conditions year-round
Susceptible grasses: Warm-season grasses such as bermudagrass, centipedegrass, and St. Augustinegrass
Solution: If overwatering is the cause, adjust your irrigation schedule. Improve drainage through aeration or grading.
8. Red Thread
Red thread disease produces thin, red filament-like threads on infected grass blades. At first glance, the irregular beige to brown patches resemble other turf diseases, but closer inspection reveals the distinctive red strands.
Timing: Spring through fall in cool, damp conditions
Susceptible grasses: Kentucky bluegrass, perennial ryegrass, fine fescue
Solution: During active outbreaks, collect and remove grass clippings to prevent spread. Apply sufficient nitrogen fertilizer.
9. Rust
Rust disease is easy to identify—just walk across an infected lawn and check your shoes. The reddish-brown fungal spores will leave noticeable stains. Although rust can discolor clothing and equipment, it often disappears with a change in weather.
Timing: Summer and fall, humid and shady conditions
Susceptible grasses: Kentucky bluegrass, perennial ryegrass, bentgrass, zoysiagrass, bermudagrass, fescues
Solution: Prune trees and surrounding plants to maximize sunlight and airflow, reducing rust persistence.
10. Slime Mold
Persistent wet weather encourages slime mold growth on grass blades. This mold can appear black, bluish-gray, yellow, brown, or white, and it interferes with photosynthesis. During extended rain, affected grass may thin and weaken, but slime mold rarely causes permanent damage.
Timing: Wet, rainy periods year-round
Susceptible grasses: All turfgrass types
Solution: Remove mold by mowing. Rake and discard clippings. Warm, dry weather helps eliminate the mold quickly.
11. Snow Mold
This disease is common in cold climates with prolonged snow cover. Snow mold (Typhula and Microdochium) creates circular gray or straw-colored patches on the lawn, ranging from a few inches to over a foot in diameter. It typically appears after snow melts in spring.
Timing: Early to late spring
Susceptible grasses: Kentucky bluegrass, tall fescue, perennial ryegrass
Solution: Rake damaged areas in spring and apply light fertilizer to encourage regrowth. Prepare your lawn in fall by removing leaves and mowing regularly until dormancy to prevent snow mold.
12. Summer Dry Patches
During hot growing seasons, dry patches measuring 3–5 inches wide may appear on the lawn. These areas often merge into irregularly shaped dead zones and are typically caused by prolonged drought stress.
Timing: Summer and hot, humid weather
Susceptible grasses: Kentucky bluegrass and fine fescue
Solution: Water lightly and frequently during drought to reduce leaf dryness. Aerate soil, reduce compaction, and encourage strong root growth.
