Brown Patch of Cool-season Lawns

Overview

Brown patch (Rhizoctonia solani) is a fungus that attacks most commonly cultivated grasses:  bent grass, perennial ryegrass, tall fescue, and annual bluegrass, but especially tall fescue. There are various species of Rhizoctonia that can attack grass plants from the seedling stage to mature plants and are pathogenic over a wide range of environmental conditions. It is common in dense, highly fertilized turf.

Brown patch may also be referred to as Rhizoctonia blight. A large brown patch is used to describe the disease in zoysiagrass. Large Patch in Zoysia Lawns

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 cool-season grasses water water-soaked circular patches that range from a few inches to several feet in diameter appear. The affected leaves wilt and turn light brown, but remain upright. A dark, grayish-black ring (smoke ring) of wilted grass is often present around the perimeter of the diseased areas in the early morning.

Life Cycle

Disease development requires the presence of an active fungus, vigorous growth of a susceptible grass, daytime temperatures ranging between 75^oF and 85^oF, the presence of free moisture on the foliage, and night temperatures below 68⁰F. 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. Avoid heavy, early spring and summer fertilization, particularly with soluble nitrogen. Avoid over fertilization of turfgrasses growing in shaded areas. 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 at the proper time of year—early fall or spring.

Organic Strategies

Strategies 2, 3, 4, 5 and 7 are strictly organic approaches. Organic lawn fertilizers are available and could be a viable organic approach to Strategy 1.

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against brown patch. Not following the pesticide label before usage is a violation of federal law.