| Brown patch (Rhizoctonia solani) is a fungus which
attacks most commonly cultivated grasses.
Differences in susceptibility exists within cultivars of
the various grass species. Bent grass, perennial
ryegrass, tall fescue and annual bluegrass are the
primary hosts. There are various species of
Rhizoctonia which can attack grass plants from
seedling stage too mature plants and are pathogenic
over a wide range of environmental conditions.
Brown patch may also be referred to as Rhizoctonia
blight. Large brown patch is used to describe the
disease in zoysiagrass.
Symptoms and Diagnosis
Symptoms vary depending on the turfgrass species
and mowing height. Susceptibility of the cultivar,
management practices and weather conditions
determine the degree of injury. More than one fungi
may also be present in the lawn.
As the name suggests, symptoms include small circular
patches of brown, lifeless grass. These patches often
enlarge and join together, reaching diameters of six feet
or more. Newly established lawns may be more
severely damaged than established lawns.
In warm-season grasses such as zoysia the most common symptom
is a circular pattern of brown grass with a yellowish
colored ring (smoke ring) of wilted grass at the
perimeter of the diseased area. The leaves can easily
be pulled from the stolons within the smoke ring
because the fungus destroys the tissue at the base of
the leaf sheath. First appearing symptoms are small
circular patches of water-soaked dark grass that soon
wilt and turn light brown. Stolons often remain
green. As the disease develops, the circular patches
enlarge, become more apparent and new green
leaves may emerge in the center of the circular
areas.
Life Cycle
Mid to late summer is the time when the best conditions are present
for disease development. This requires the presence
of an active fungi, vigorous growth of a susceptible
grass, daytime temperatures ranges between 75
degrees and 85 degrees F, the presence of free
moisture on the foliage and night temperatures
below 68 degrees F. This fungus feeds on dead
organic matter in the soil, but will attack grass when
the right environmental conditions arise. Hot, humid
conditions promote spread of the fungi.
Integrated Pest Management Strategies
1. Fertilizer. Don't fertilize warm-season grasses in early spring and summer, particularly with soluble nitrogen.
Use slow-release nitrogen
fertilizers. Fertilize to maintain adequate but not
lush growth during the growing season. Properly
fertilized turf will recover quicker from disease
injury than will under-fertilized turf.
2. Collect waste. Remove and dispose of clippings
from infected areas or when conditions are
conducive to disease development. Mulching
mowers that chop clippings to 1/4 inch or less do
not contribute to brown patch development.
Mow only when the grass is dry, being sure to
remove no more than one third of the top growth.
3. Prune. Prune trees and shrubs to allow air
movement and light penetration to reach
the turfgrass.
4. Watering. Water to a depth of about 6 inches
no more than once a week. More frequent
watering provides an ideal environment for
disease development.
5. Drainage. Provide good surface and subsurface
water drainage to reduce humidity in the
turf canopy.
6. Fungicide. Use a preventive fungicide program
with recommended fungicides. Read labels for
proper fungicides and their use.
7. Replant dead areas. The disease can occur
quickly, spread rapidly and then stop abruptly as
environmental conditions change. Frequently, the
best and only recourse is to replant dead areas in warmseason
lawns in early summer. | 
