Types of Lawn Diseases
Spring-Through-Fall Lawn Diseases
Fairy Rings
Caused by more than 50 varieties of fungus, the rings vary in size and appearance but all form in soil that is high in woody, organic matter, usually from buried debris or tree stumps.
Look for: Rings of fast-growing, dark-green grass with centers of weeds, thin turf, or dead grass. Midsummer and fall rings are more apt to be composed of dead grass.
Management: The rings are difficult to remove unless completely dug out to a minimum depth of 1 foot. Aerating the ring area to improve water penetration and fertilizing to minimize color variation are helpful.
Stripe Smut
The disease causes yellowed, stunted growth in 6- to 12-inch patches.
Look for: Development of characteristic black stripes of erupted spores along grass blades that later become dry, shredded, and curled.
Management: Maintain adequate fertilization. Water well; mow frequently; and bag clippings. If the disease persists, stop wasting time and money on fungicides. Upgrade your lawn to a newer, disease-resistant cultivar instead. Consult your Cooperative Extension Service for the best cultivar for your locale.
Necrotic ring spot
Although the fungus is active during cool, moist periods, the damage frequently doesn't show until later, when turf is stressed.
Look for: Circular "frog-eye" patterns of 6 to 12 inches with matted, straw-colored grass surrounding a tuft of green grass. As infection advances, roots and crowns may turn brown to black. Thatch may decompose in affected areas, giving them a sunken, or "donut," appearance.
Management: Overseed with disease-resistant cultivars of tall fescue and perennial ryegrasses, or use bluegrasses. Water to lessen drought and heat stress. Avoid excessive fertilizer use. Remove excess thatch, and maintain adequate aeration and drainage.
Drechslera melting-out and leaf spot
Exhibiting two phases, the disease is especially destructive on over-fertilized, lush bluegrasses. Cloudy, moist weather in the 70° to 85°F range brings on the telltale leaf-spot phase.
Look for: Distinctive dark purple spots that develop into buff-colored oval lesions with a dark brown or purple margin. Blades progress to yellow and then rum tan. During the melting-out phase, rot develops in roots and crowns.
Management: Avoid excessive nitrogen fertilizer; water infrequently but deeply; mow high; aerate; and remove excess thatch. If the disease persists, upgrade your lawn to a disease-resistant cultivar.
Summer Lawn Diseases
Brown patch
The disease is prevalent during moist, hot weather on over-fertilized lawns.
Look for: Dark, water-soaked-looking grass turning to browned-out circular areas several inches to sev-
eral feet in diameter. Frequently some green leaves persist within the patch, and roots remain intact. Blades may have irregular ash gray lesions with a dark brown margin running along one side. On short turf, a 2-inch "smoke ring" of gray mycelium may encircle the patch in early morning.
Management: Water deeply but infrequently; mow high; remove excess thatch; and improve aeration and drainage.
Dollar spot
Affects low-nitrogen lawns, especially when stressed by drought and when heavy dews are prevalent.
Look for: Mottled, straw-colored 4- to 6-inch patches on lawns with taller grass. Grass blades have light tan bands with reddish brown margins spanning across them. Patches may merge to form large, irregular areas. Grayish white cobweb-like mycelium may be present in early morning.
Management: Maintain adequate nitrogen and potassium fertility; water deeply when necessary; and remove excess thatch. If your grass is prone to dollar spot, remove morning dew by dragging a hose across the lawn. Or overseed with a blend of improved cultivars.
Pythium blight
A serious, rapidly spreading disease involving the entire grass plant, pythium blight occurs on poorly drained soils that have a wet grass canopy. Look for it when nighttime temperatures plus relative humidity equals 150.
Look for: The sudden appearance of 1- to 6-inch reddish brown, wilted patches, which turn to streaks as they enlarge along drainage patterns. In early morning, the grass is slimy, dark, and matted. White cottony mycelium may be present when grass is wet. As it dries, the grass turns light tan and shrivels.
Management: Improve drainage and air circulation; avoid overwatering; aerate; reduce excess thatch; and avoid nitrogen fertilizer during warm weather. Check calcium levels, and add lime if deficient. Observe closely for spread, and consult your Cooperative Extension Service if the disease progresses.
Rust
Appears on low-fertility, compacted, or shady lawns when growth slows during hot, dry weather.
Look for: Initial small yellow flecks that develop into pustules releasing yellow, orange, red, or dark brown spores. From a distance the turf appears orange or yellow, and colored spore residue rubs off if touched.
Management: Provide appropriate fertilization and irrigation; prune low-hanging tree branches to reduce shade; maintain aeration; and mow frequently, bagging clippings. Upgrade your lawn with a rust-resistant cultivar if the disease persists.
Fall-Through-Spring Lawn Diseases
Typhula blight (gray snow mold)
Strictly a cold-weather disease, typhula blight appears where snow cover has melted, especially in areas where snow has drifted or been piled.
Look for: Irregular 2- to 24-inch patches of bleached-out, matted turf covered with moldy, grayish white mycelium. Tiny black or orange-brown spherical sclerotia (hard fungus bodies) may be observed imbedded in the leaves and crowns of infected plants.
Management: Avoid heavy nitrogen fertilization in late fall to allow new growth time to harden off before winter. Keep thatch to a minimum and grass height lower as winter begins. Avoid piling snow onto your lawn, and prevent compaction on important turf areas by limiting activity on them when they're covered with snow. Rake in early spring to promote drying and reduce matting. Provide a light spring fertilization if damage is present.
Fusarium patch (pink snow mold)
This disease develops from late fall to early spring during cool, moist, cloudy weather, with or without snow cover.
Look for: Small, light tan to rusty brown circular patches that may grow to 2 feet and become ringlike as interior grass re-grows. When the grass is moist, salmon-colored mycelium is visible in sunlight. There are no sclerotia present.
Management: Fertilize in late fall, once grass growth ceases, with a slow-release nitrogen fertilizer. Mow the lawn; keep thatch low; and don't allow leaves or debris to remain on the lawn over winter. Rake the lawn well in early spring, and follow with a light fertilization if damage is present. As with any older, disease-prone lawn, consider upgrading to one of today's high-tech cultivars. You may be able to make a gradual transition by over-seeding in successive years, or you may need to remove the existing turf for replanting.