Brown Patch of Turfgrass
"Every year my lawn develops brownish areas, where dead grass blades are mixed with green blades. Sometimes there appears to be a circular pattern to the areas, but not always. I think this is a disease problem, but haven't had success getting rid of it. What do you recommend?"
Brown Patch is a common turf disease that occurs every year in eastern Nebraska and is caused by the fungus Rhizoctonia solani. In home lawns, Brown Patch is usually found on bluegrass, tall fescue, perennial rye and zoysia grass.
Symptoms of Brown Patch start with scattered dead grass blades forming a circle or semi-circular pattern in the lawn. The circles of affected grass may be up to 2 feet in diameter, although they can be smaller as well. Close examination of the leaves shows long, irregular leaf spots that are light tan or whitish in color. The margins of leaf spots are dark brown or purplish-black. Grass in the center of the circles may not show any disease symptoms at all.
Brown Patch occurs most commonly on dense, heavily fertilized and watered lawns. Hot, humid weather with day temperatures of 85 degrees or above and night temperatures over 60 degrees are most conducive to the development of Brown Patch. Poorly drained soil, excessive thatch and evening irrigation all increase a lawn's susceptibility to the disease by lengthening the amount of time the leaf blades are wet and providing good conditions for the growth of the fungal spores. Lawns that are heavily fertilized in the spring, put on lush, succulent growth that is very susceptible to disease. Using a dull mower blade will also increase the turf's susceptibility to infection, because the dull blade shreds the ends of the grass blades and creates large wounded areas for fungal spores to enter. A sharp mower blade makes a quick, even cut with a smaller surface area for infection.
Brown Patch can be controlled by the application of fungicides like benomyl, chlorothalonil and maneb. These chemicals will protect new grass blades as they emerge from becoming infected. It will take several weeks before the turf can put on enough growth that the damaged areas are no longer visible. During this time, a homeowner can also reduce the severity of the disease with the following techniques.
- Water the lawn in the morning and only make two applications of water per week. Apply a half-inch of water at a time. Bluegrass lawns may need an additional application of water in the very hottest parts of July and August.
- Remove and dispose of grass clippings from infected areas of the lawn.
- Frequently sharpen the mower blade.
Brown Patch Disease of Turfgrass, University of Nebraska-Lincoln Extension