Patch Diseases Serious Problem
Perhaps the most serious turf disease likely to occur in northern
Illinois is summer patch and necrotic ring spot,
two separate diseases that attack grass roots and previously were
referred to as fusarium blight. Research continues to look for
information on these diseases. Brown patch may also attack
turfgrasses. These "patch diseases" are similar in appearance
and management in lawns.
Rings of dead grass are typical symptoms
of patch disease.
Summer patch and brown patch tends 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 turf stress in
summer, however. Crescent shaped or circular patches of dead grass,
often with clumps of green grass inside, are a characteristic
symptom (often called "frogeye"). Lawn and other turf
areas with advanced disease development may show irregular dead
areas and streaks.
Patch diseases typically develop on turf with stress factors
such as excessive thatch, poor soil conditions, sod installed
over a poorly prepared site, irregular/excessive nitrogen fertility,
and related problems. One typical situation in which these diseases
occur 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 condition leads to
poor root penetration and development, and also often a problem
Management of these 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,
mowing (avoid mowing too short), and watering are suggested. Spring
and fall are suggested times for aerifying, assuming the turf
is actively growing. Avoid heavy spring applications of nitrogen
fertilizer. Focus most applications on the fall period. Fertilizers
containing controlled-release nitrogen are suggested. Overseed
dead areas with perennial ryegrass and resistant Kentucky bluegrass
cultivars in late August or early September.
These management suggestions may not bring immediate results,
but will get the patch disease 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.
Written by Bruce Spangenberg, former Extension
Educator, Horticulture. University of Illinois Extension.