The beauty of a lawn can be quickly destroyed by brown patch (Rhizoctonia species), a serious fungal disease that can affect all South Texas lawn grasses. It can develop rapidly when temperatures are warm (70° to 90° F) and humid, especially during warmer periods of the fall and winter months. Warm-season grasses such as St. Augustine (especially the over-planted ‘Raleigh’ selection), Bermuda, and Zoysia are most commonly affected by brown patch (also called large patch) during the early spring and late fall.

Symptoms
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. Augustine grass grown in shady, moist locations.

Close inspection of grass blades reveals small, irregular, tan leaf spots (burnt cigarette appearance) with dark-brown borders in combination of rotted leaf sheaths near the soil surface.

Grasses Commonly Affected
All types of lawn grasses grown in South Texas can be affected by brown patch. There are no turfgrass species currently available that are entirely resistant to brown patch. Brown patch is the most common and important disease of ‘Raleigh’ St. Augustine in this area. In most cases, affected areas are able to recover, but the selection of Flora-TAM (St. Augustine) shows the most potential for being highly resistant.

Prevention and Treatment
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.

Avoid high nitrogen rates on warm season grasses in mid to late fall. The brown patch fungus readily attacks the lush growth of grass which nitrogen promotes. The use of Texas greensand as a supplement when fertilizing will help adjust the soil pH, thus making essential nutrients readily available. Apply Texas greensand at a rate of 10 pounds per 1000 square feet.

Irrigate grass only when needed and to a depth of 4 to 6 inches. Water early in the morning. This disease can spread fast when free moisture is present.

Avoid spreading the disease to other areas. Remove clippings if the weather is warm and moist to prevent spread to other areas during mowing.

Keep lawns mowed on a regular basis to the proper height for the grass species you are growing. Prevent excessive thatch buildup.

Provide good drainage for both surface and subsurface areas.

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 warm-season grasses is to initiate fungicide sprays when nighttime low temperatures reach 70° F. Stop applications when nighttime 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. Alternate fungicides to prevent buildup and resistance to the chemical. Slightly better control may be obtained by a liquid fungicide application rather than by granular application.

Table 1. Chemicals for Control of Brown Patch

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

Remember, Learn and Have Fun!

David Rodriguez is the County Extension Agent-Horticulture for Bexar County. He represents Texas Cooperative Extension with the Texas A&M University System. For any landscape or gardening information, call the Bexar County Master Gardeners Hotline at (210) 467-6575, e-mail questions to mg-bexar@tamu.edu, or visit our County Extension website at http://bexar-tx.tamu.edu/.

Special Note: Listen to live broadcast of the Home & Garden Show with David Rodriguez & Bill Rohde on WOAI 1200 AM, every Saturday morning between 8:00-11:00 a.m., and call in your gardening questions at (210) 737-1200 or 1-800-383-9624. Check it out!