These articles are written to apply to the northeastern
corner of Illinois. Problems and timing may not apply outside of this
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 25 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.