Symptoms:

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.

Sympoms of brown patch on turfgrass. Photo from the Maryland Cooperative Extension.

Season:

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.

Disease Cycle:

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.

Cultural Management:

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.

Chemical Management:

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