Brown Patch Disease of Lawns

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The beauty of a lawn can be quickly destroyed by brown patch (Rhizoctonia species), a serious fungal disease that can affect all South Carolina lawn grasses. It can develop rapidly when temperatures are warm (75 to 90 °F) and humid, especially on cool-season grasses (fescue, ryegrass, bluegrass and bentgrass). It can also occur on these grasses during warmer periods of the winter months. Warm-season grasses (St. Augustinegrass, zoysiagrass, Bermudagrass and centipedegrass) most commonly are affected by brown patch (also called large patch) during the early spring and late fall.

Symptoms of brown patch may vary greatly with the type of grass and soil conditions. The disease usually causes thinned patches of light brown grass that are roughly circular in shape. These areas range in diameter from a few inches to several feet. Often the center of the patch will recover, resulting in a doughnut-shaped pattern.

When disease conditions are favorable, large areas of the lawn may be uniformly thinned and eventually killed with no circular patch being evident. This type of pattern is commonly seen on infected St. Augustinegrass grown in shady, moist locations.

Close inspection of cool-season grass blades reveals small, irregular, tan leaf spots with dark-brown borders. Bentgrass may not show individual lesions, but leaves will turn brown and shrivel. Infected warm-season grasses rarely have leaf spots but instead have rotted leaf sheaths near the soil surface.

All types of lawn grasses grown in South Carolina can be affected by brown patch. There are no turfgrass species entirely resistant to brown patch currently available. Brown patch is the most common and important disease of tall fescue in the Southeast. In most cases affected areas are able to recover, but tall fescue lawns less than a year old can be completely killed.

The best way to prevent brown patch in the home lawn is by following good lawn care practices. This is much easier and less expensive than the use of fungicides and can be very effective.

Fungicides can be difficult to rely upon for controlling brown patch in the home lawn but regular applications can vastly improve appearance. A good "rule of thumb" to follow on either cool- or warm-season grasses is to initiate fungicide sprays when night time low temperatures reach 70 °F. Stop applications when night time lows are forecast to be below 70 °F for five consecutive days. Typically, applications are made at 14-day intervals. If disease is severe enough to warrant chemical control, select one of the following fungicides listed in Table 1. It may help in control to alternate fungicides used with subsequent applications to prevent a buildup of resistance to a fungicide. Slightly better control may be obtained by a liquid fungicide application rather than by granular application.

* Due to product cost and for accurate application, homeowners may want to hire a licensed landscaper to apply products containing these fungicides.