University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Patch Diseases Appear
on Home Lawns in Summer

July 6, 2000

Hot summer weather can cause a variety of problems for lawns, including heat stress, drought stress, crabgrass explosions, and patch disease. Patch diseases, formerly referred to as fusarium blight, often appear during the heat of summer on lawns. Patch diseases include summer patch, brown patch, and in some areas, necrotic ring spot.

Crescent shaped or circular patches of dead grass, often with clumps of green grass inside, (often called "frogeye") are a characteristic symptom of patch diseases. Summer patch and brown patch tend to be most active in hot weather, while necrotic ring spot tends to be most active in late spring and in fall. Disease symptoms often show under lawn stress in summer, however. Lawns with advanced disease development may show irregular dead areas and streaks.

Lawns with various stress problems typically are the ones that develop patch diseases. These underlying problems include excessive thatch, poor soil conditions, sod installed over a poorly prepared site, irregular/excessive nitrogen fertility, and similar problems. One common problem scenario is recently sodded lawns (within 2–5 years) put down over a clay soil, usually with good care (high watering & fertility) to keep the grass green and vigorous. This leads to poor root penetration and development, and also often a thatch problem.

Management of patch diseases consists of correcting soil problems and implementing proper cultural practices, overseeding dead areas, and possibly fungicide applications. Improving conditions for root growth and reducing problem thatch is critical. Practices such as core aerifying and topdressing, along with sound fertilizing and watering, are suggested. Light, frequent irrigation may help reduce stress of summer patch.

Mow around three inches for the summer. Overseed dead areas with perennial ryegrass and resistant Kentucky bluegrass cultivars in late August or early September. Fall and spring are suggested times for core aerating.

These management suggestions may not bring immediate results, but get patch diseases under control in the long run. Fungicides are an option to help prevent further development on unaffected grass but will not reverse the factors causing the disease or eliminate the disease. Fungicides treat the symptoms but not the cause of the problem.


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