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University
of Rhode Island GreenShare Factsheets
Turf
Diseases: Rhizoctonia Brown Patch
The
name "brown patch" best describes symptoms of this disease
on low-cut turfgrass, such as golf greens, but the same fungus
can
cause similar, though distinct, symptoms in lawns. Expanding patches
of discolored grass up to several feet in diameter mark the
presence
of a severe outbreak. The affected turf may turn brown primarily
at the leading edge of the patch while the grass in the center,
though thinned, may remain green. Diseased areas are sometimes
diffuse
and not so clearly circular. On individual grass blades, lesions
of various sizes occur which have bleached centers and purplish-brown
margins. Where disease is severe, the affected area may look
sunken.
When dew or other moisture is present on the turfgrass, the gray,
weblike mycelium of the fungus may be visible. In rainy weather,
or where moisture persists on leaves because of poor air circulation,
abundant white mycelial growth may be observed. The fungal
growth
associated with Pythium blight is
similar in appearance, but the leaf blades are more matted and
greasy looking
than those infected with the brown patch fungus. Brown
patch is a disease of hot, humid weather. It is most common when
night temperatures and relative humidity stay high for several days
and are accompanied by rain. Disease development can be very rapid
under such conditions. In
hot, humid weather the fungus Rhizoctonia solani becomes
active. It grows well in thatch and soil. The survival structures
germinate and produce grayish to brown mycelium that is capable
of infecting the grass blades. Infection is most severe when the
grass is succulent from nitrogen fertilization and when leaf surfaces
remain wet from frequent irrigation or rain.
There are two important cultural practices that will limit brown
patch in lawns: 1)
Excessive nitrogen applications cause a flush of succulent growth
that is very susceptible to brown patch. Avoid nitrogen fertilizer
applications just before or during hot weather. Several lighter
fertilizer applications are less likely to trigger disease than
one heavy application. 2)
Water on turfgrass leaf blades greatly increases infection and disease.
If the lawn needs moisture, water to a depth of 6 inches early in
the day, so the grass leaves will dry quickly. Do not water in the
late afternoon or early evening. Night watering is not recommended
in hot, humid weather. Avoid frequent light sprinklings. Brown patch
is most severe in bentgrass, perennial ryegrass, and tall fescue
lawns. Turfgrass cultivars that are more resistant or tolerant to
brown patch are available for establishing lawns or reseeding damaged
areas. When
a lawn has had previous brown patch
problems, fungicides may be applied when humid weather and hot nights
are predicted. Applications should continue according to the fungicide
label for as long as the hot, humid weather persists. Fungicides
are usually not necessary on Kentucky bluegrass/fine fescue lawns.
Adapted from the UMass Extension,
2000
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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