No doubt about it, brown patch is the most damaging disease of warm-season turfgrasses in Georgia. Many turfgrasses, including, tall fescue, 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 F.
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.
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 attacked by the brown patch fungus, Rhizoctonia solani, first become water-soaked and wilted, finally turning brown.
Control measures: 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 reduce disease outbreaks during the late winter and early spring, avoid fall applications of nitrogen fertilizer. During periods of active disease infection, stop all applications of nitrogen. Finally, maintain phosphorous and potash levels according to soil test recommendations.
Moisture also plays an important role in disease development. Good drainage is needed to remove excess water. To improve drying 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 the foliage stays wet.
Thatch often harbors brown patch. Periodic mechanical dethatching or core aerification is needed to prevent thatch buildup, especially on bermuda grass and zoysia grass lawns.
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 seven- to 10-day intervals to the diseased area and to a one- to two-foot border.
Keep in mind that, not one, but several applications of a recommended fungicide will be necessary to adequately control brown patch.
Michael Wheeler is the Hall County extension coordinator. Phone: 770-531-6988. Fax: 770-531-3994. His column appears Fridays and on gainesvilletimes.com.