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.
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.
Strategies 2, 3, 4, 5 and 7 are strictly organic approaches. Using an appropriate organic fertilizer would be a viable organic approach to Strategy 1.