No doubt about it, Brown Patch is the most damaging disease of warm-season turfgrasses in Georgia. All of the turfgrasses grown in Cherokee County, including St. Augustine grass, Centipede grass, Zoysia grass and Bermuda grass are susceptible to this fungal disease. Excessive nitrogen fertility levels and thatch often lead to outbreaks of Brown Patch. This disease usually develops on lawns during periods of wet, overcast weather in late spring or early summer and again in the fall. Damage is often heaviest after several days of showers with daytime temperatures of 70 to 80 degrees Fahrenheit.
Brown patch first appears in lawns as small, circular, brown areas several inches in diameter which may then quickly increase to 3 to 6 feet across. These areas often grow together, forming irregular patches of brown, blighted turf up to 20 feet in diameter. The foliage of high-cut St. Augustine grass and centipede grass often wilts and collapses, giving the blighted patches a sunken appearance. Damaged turf usually recovers when conditions no longer favor the spread of the disease. Regrowth of the turf usually starts in the center of the blighted area, forming a ring or frog-eye pattern. Weeds may invade turf damaged by Brown Patch. Damage to individual grass plants is usually confined to the foliage, although in severe cases the disease infects and kills the stems, stolons and roots. Leaves attached by the Brown Patch fungus, Rhizoctonia solani, first become water-soaked and wilted, finally turning brown. On broadleaf turf grasses, like centipede grass, distinct tan-colored leafspots that are surrounded by water-soaked margins are sometimes seen. If the crowns or stolons are infected, large areas of a lawn may be killed.
Nitrogen fertility has a significant impact on brown patch development. High nitrogen levels promote the growth of soft, succulent leaves that are susceptible to attack by the Brown Patch fungus. To help prevent disease outbreaks, apply a low rate of a nitrogen fertilizer at four- to eight-week intervals or use a slow-release nitrogen source to maintain an even growth rate. To reduce disease outbreaks during the late winter and early spring, avoid fall applications of nitrogen fertilizer. During periods of active disease infection, curtail all applications of nitrogen as nitrogen encourages further spread of the disease. Finally, maintain phosphorous and potash levels according to soil test recommendations. Every three years, and particularly when your lawn is having a problem, I recommend a laboratory soil test. The University of Georgia’s Soil Lab will do an excellent test and give you specific recommendations for you type of lawn. It’s a bargain at $9 per sample.
Moisture also plays an important role in disease development. Good drainage is needed to remove excess water. To speed evaporation of water from the foliage, prune nearby trees and shrubs to reduce shade and improve air movement. Also, irrigate lawns at times that minimize the amount of time that the foliage remains wet. We can’t control the rain, but we can set our irrigation systems to water during the night or very early morning.
Thatch often harbors the Brown Patch fungus. Periodic mechanical dethatching or core aeration is needed to prevent thatch buildup, especially on St. Augustine grass and Zoysia grass lawns. Outbreaks of Brown Patch occurring on thatch-heavy lawns are likely to reoccur and cause damage in following years unless the thatch is properly removed.
On most home lawns, a fungicide spray program should begin as soon as symptoms appear and continue until the turf starts to recover or until weather conditions no longer favor the spread of disease. To avoid serious damage, begin applications as soon as symptoms appear. For effective control, apply fungicides at five- to seven-day intervals to the diseased area and to a 1 to 2 foot border. Make applications only when weather conditions favor the spread of disease. The time interval between applications varies between 10 to 21 days, depending on the fungicide used. Keep in mind that, not one, but several applications of a recommended fungicide will be necessary to adequately control Brown Patch.
Information about Extension Solutions for Homes and Gardens can be found on the UGA extension website, www.caes.uga.edu/extension/cherokee ; or contact the Cherokee County Extension Office, 1130 Bluffs Parkway, Suite G49, Canton, GA, 30114, 770-721-7803.