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Common Lawn Diseases

Dollar spot



Dollar Spot in BermudagrassSymptoms: small, circular spots from 1–5 inches in diameter; spots might merge to form large, irregular areas; leaves appear watersoaked then brown, often exhibiting a reddish band across the leaf; fine, white cobwebby threads seen in early morning


Susceptible grasses: bermudagrass, annual bluegrass, fescue, ryegrass, Seashore paspalum, zoysiagrass


Conditions favoring disease: moderate temperatures (60°–80°F); excess moisture or water stress; fog; thatch; survives in soil as hard, dark structures (sclerotia)


Prevention: fertilize adequately; reduce thatch; water appropriate length of time to a depth of 4–6 inches but don’t extend interval too long; maintain air circulation; compost top dressings can suppress disease


Chemical treatment: if present in previous years, fungicides might be useful; apply in early spring or fall before symptoms occur

 

Fairy Ring



Fairy Rings in Lawn Symptoms: a dark green band of turf develops in a circle (4 inches up to 30 feet) or semicircle in moist turf; mushrooms might or might not be present; an area of brown, dying grass might occur just behind the dark green band; a second ring of dying grass might appear inside the circle; weeds commonly invade


Susceptible grasses: all lawn grasses


Conditions favoring disease: soils high in thatch or undecomposed organic matter containing lignin


Prevention: apply adequate nitrogen; aerate soil for better water penetration, water heavily in holes for several days; verticut if more than 1/2 inch of thatch accumulates; rake mushrooms to improve appearance of turf; to eliminate, remove turf and root zone containing white, cottony mass to a depth of 12 inches and 2 feet beyond outer edge of the ring; refill with clean soil and reseed or resod


Chemical treatment: fungicides available, but control has been erratic

 

Fusarium Blight



Fusarium BlightSymptoms: small, circular, grayish green areas, ranging from a few inches up to a foot in diameter; some plants in center can survive, giving a frog-eye appearance; the crown or basal area of dead stems has a reddish rot and is hard and tough; dead foliage appears bleached


Susceptible grasses: Kentucky bluegrass


Conditions favoring disease: daytime temperatures of 85°–95°F; drought-stressed areas in full sun; survives in thatch and grass residues


Prevention: water appropriate length of time; don’t apply more than 1 pound nitrogen/1,000 square foot/application or more than 6 pounds annually; use a mixture of 20% perennial ryegrass when seeding bluegrass; mow at highest recommended height; verticut if more than 1/2 inch thatch


Chemical treatment: fungicides don’t give complete control; make application in spring before or just after symptoms appear

 

Gray Leaf Spot



Grey Leaf Spot in St. AugustinegrassSymptoms: irregular blighted patches of turf with bleached spots with dark margins on leaves; ryegrass develops a fishhook appearance


Susceptible grasses: fescues, kikuyugrass, ryegrasses, St. Augustinegrass


Conditions favoring disease: daytime temperatures of 85°–95°F; high humidity or rainfall; overwatered and overfertilized turf


Prevention: irrigate properly; don’t overfertilize; reduce shading; increase air movement


Chemical treatment: fungicides are available, but cultural controls are more practical

 


Microdochium Patch (pink snow mold)



Microdochium Patch (pink snow mold)Symptoms: circular patches of 1–2 inches that can enlarge to 12 inches; leaves first appear watersoaked, then reddish brown, and finally bleached; minute, gelatinous spore masses sometimes seen on dead leaves; white or pinkish fungal threads might be seen in early morning


Susceptible grasses: annual bluegrass, bluegrasses, fescues, ryegrasses, zoysiagrass


Conditions favoring disease: consistently cool temperatures (40°–65°F) and wet conditions; high nitrogen applications in fall; neutral or alkaline soil pH; pathogen survives in grass residues


Prevention: reduce shade and improve soil aeration and water drainage; water appropriate length of time; avoid excess nitrogen, especially in fall; maintain soil pH between 6.5–6.7.


Chemical treatment: if a serious problem in past, apply fungicides in fall before symptoms appear

 

Leaf Spot



Leaf Spot Symptoms: circular to elongated brownish spots with brown centers and dark brown or purple borders on leaf blades, sheaths, and stems; crowns and roots frequently have a dark brown rot; crown-infected plants might die in hot, windy weather, leaving thinned areas throughout the turf; spores are windborne


Susceptible grasses: bermudagrass, bluegrasses, fescues, kikuyugrass, ryegrasses, zoysiagrasses


Conditions favoring disease: warm temperatures (70°–90°F) for bluegrasses, ryegrasses, and fescues; cool temperatures (60°–70°F) for bermudagrass and zoysiagrass; high humidity; low clipped turfgrass; most severe with excess nitrogen fertilization or deficiency


Prevention: reduce shade; improve soil aeration and water drainage; avoid dry spots and too much nitrogen fertilizer; maintain as high a cutting height as possible


Chemical treatment: fungicides available but often not warranted


Pythium Blight (Grease spot)



Pythium Blight on Lawn Symptoms: small, circular spots (2–6 inches) that run together; blackened leaf blades rapidly wither, turn reddish brown, lie flat, stick together, and appear greasy; roots might be brown; in humid conditions, masses of fungal mycelium might appear


Susceptible grasses: all grasses


Conditions favoring disease: low spots that remain wet; warm temperatures (80°–95°F daytime, >68?F night time); survives as spores in soil for long periods


Prevention: reduce shading; improve soil aeration and water drainage; water appropriate length of time; avoid mowing wet grass and applying high levels of nitrogen during hot, humid weather

Chemical treatment: fungicides available but primarily prevented by cultural practices


Rhizoctonia Blight



Rhizoctonia Blight Symptoms: first appears as small, irregular brown patches or rings that can enlarge to many feet in diameter; centers might recover resulting in rings of diseased grass; leaves and sheaths become watersoaked, wilt, turn light brown, and die; in light infestations, roots usually not infected and plants often recover; soil-inhabiting fungus that forms fine, fungal threads in soil or on turfgrass


Susceptible grasses: bluegrass, annual bluegrass, fescues, ryegrasses


Conditions favoring disease: excess thatch and mat along with high temperatures (80°–95°F); high humidity; soft, lush growth due to excessive nitrogen; most common in warm, inland areas


Prevention: reduce shading and improve soil aeration and water drainage; water appropriate length of time to a depth of 4–6 inches; avoid excess nitrogen; maintain thatch less than 1/2 inch


Chemical treatment: fungicides useful if disease severe in past or for seedlings in young turf

 

Rhizoctonia Large or Brown Patch



Large Patch Symptoms: first appears as small, irregular brown patches or rings that can enlarge to many feet in diameter; centers might recover resulting in rings of diseased grass; leaves and sheaths become watersoaked, wilt, turn light brown, and die; plants pull out easily from soil with rotten stolons, in light infestations, roots usually not infected and plants often recover; soil-inhabiting fungus that forms fine, fungal threads in soil or on turfgrass


Susceptible grasses: bermudagrasses, kikuyugrass, St. Augustine grass, zoysiagrass


Conditions favoring disease: excess thatch and mat along with cool temperatures (60°–70°F); wet soil conditions


Prevention: reduce shading and improve soil aeration and water drainage; water appropriate length of time to a depth of 4–6 inches; avoid excess nitrogen in the fall; maintain thatch less than 1/2 inch


Chemical treatment: fungicides useful if disease severe in past


Red Thread



Red Thread Symptoms: red thread may kill turfgrass in patches that are 2–8 inches in diameter, or the disease may occur over large areas without killing the plants; pink web of fungal threads bind the leaves together; look for pink, gelatinous fungal crusts projecting from the leaves to help identify this disease


Susceptible grasses: bentgrasses, bermudagrasses bluegrasses, fescues, ryegrasses


Conditions favoring disease: common under conditions of mild air temperatures (60°–75°F) and extended periods of leaf wetness; often appears on plants deficient in nitrogen during periods of cool or warm temperatures if there is adequate moisture (e.g., excess irrigation or rainfall)


Prevention: proper irrigation and fertilization can reduce the incidence; adequate nitrogen usually can prevent this disease from occurring; prevent drought stress by irrigating turfgrass based on evapotranspiration needs of the turfgrass; provide adequate air circulation; reduce shading


Chemical treatment: fungicides rarely warranted except in severe cases

 

Rust



Symptoms: irregular patches of weak turf covered with rust colored growth (spores)


Susceptible grasses: all grasses


Conditions favoring disease: moderately warm air temperatures (70°–75°F) and extended periods of leaf wetness favor development; turf that is deficient in nitrogen is more susceptible


Prevention: maintain turfgrass vigor by following proper irrigation and fertilization requirements for turf species; mow regularly and remove clippings to reduce number of spores if lawn is infected


Chemical treatment: follow proper cultural practices; fungicides shouldn’t be needed

 

Spring Dead Spot



Spring Deas Spot Symptoms: circular areas of dead grass 6–12 inches in diameter appear in spring when growth resumes; spots might coalesce to form large areas; typically affects turfgrass more than 2 years old


Susceptible grasses: bermudagrass, Seashore paspalum, zoysiagrass

 

Conditions favoring disease: affects dormant plants; most severe when soil temperatures are < 65°F; survives as sclerotia and in infected roots and stolons


Prevention: remove dead grass; fertilize in summer to maintain vigor; don’t overfertilize in late summer; water appropriate length of time


Chemical treatment: fungicides available but primarily prevented by cultural practices

 

Summer Patch



Summer Patch Symptoms: circular, yellow or tan areas of dead and dying plants up to 1 foot in diameter; can have green, apparently healthy plants in center; roots, crowns, and stolons have dark brown fungal hyphae on them; vascular discoloration and cortical rot occur in later stages


Susceptible grasses: bluegrasses, fine fescues


Conditions favoring disease: high temperatures (> 85°) in late spring through the summer; most severe when turf is mowed low or when soil moisture is excessive


Prevention: aerate soil and apply slow-release nitrogen; improve drainage; reduce compaction; water appropriate length of time; don’t mow too low; control thatch; reduce soil pH if higher than 7

 

Chemical treatment: systemic fungicides in fall usually necessary when disease has been severe