COLUMBIA, Mo.—Homeowners who see parts of their lawn turning brown may reach for a garden hose, thinking the grass needs a drink. But that might just make the problem worse, warns a University of Missouri Extension regional agronomist.

Before watering, make sure the browning isn’t the result of a fungal disease called brown patch, said Ted Fry.

Caused by the fungus Rhizoctonia solani, brown patch is prevalent in warm, humid areas.  It attacks different species of grass, including St. Augustine, Kentucky bluegrass and fescue. Excessive watering can speed the growth of the fungus.

The disease first appears as small, brown spots but can spread quickly in warm weather. Patches may look like doughnuts, with a ring of brown encircling an area of green grass.

“Brown patches from one to several feet across develop in a day or two,” Fry said.

Fluffy fungal webbing is sometimes visible in the infected grass in the morning when dew is on the ground. Leaves have oblong, irregularly shaped lesions.

To suppress brown patch, water only two to three times a week so the leaves receive from one to one-and-a-half inches in total irrigation, he said. Don’t water in the evening; lawns left wet overnight in warm weather are more susceptible to disease.

Mow regularly with a sharp blade at 2.5 to 3 inches or more. Do not fertilize heavily with nitrogen.

A number of fungicides are available, though these products can be expensive.  If you decide to use a fungicide, always follow product label instructions.

“Unless other stress occurs, the grass will recover later in the summer or fall when night temperatures decrease and cooler rains arrive,” Fry said.

For more information, see “Brown Patch Management in Tall Fescue Lawns” in the July 2011 issue of the MU Integrated Pest Management Program's Missouri Environment & Garden newsletter.