With the onset of hot, humid summer weather in the Midwest and Mid-Atlantic region lawns become susceptible to a disease called brown patch. Lawns consisting of tall fescue or perennial ryegrass are the most susceptible to brown patch. When looking for signs of the disease, the name brown patch can be a little deceiving. In a home lawn mowed at 2 to 3 inches the disease will appear as diffuse areas of turf that is brownish colored.
Brown patch (Rhizoctonia solani) is caused by a fungus and when weather conditions become favorable it infects the turfgrass plants. Brown patch thrives when the daytime temperature is above 80°F and the nighttime temperature is above 65°F, the humidity is high and there is ample moisture. The rest of the year the brown patch fungus is in a dormant state in the soil.
Brown patch infects only the leaf blades. If you examine several individual tall fescue leaf blades closely, you will see tan blotches surrounded by a dark brown or black border. As the disease progresses the blotch may extend across or down the leaf blade. The leaf tips die and turn brown giving the turfgrass an overall brown color.
Damage from brown patch ranges from cosmetic damage resulting in unsightly turf for 2 or 3 weeks during the heat and humidity, to severe loss of turf if the hot, humid, wet weather extends for a longer period of time.
Managing brown patch can be a challenge since homeowners don’t have any control over the temperature or humidity. Maintaining turf on the dry side of the moisture spectrum is a good idea. If you must water, extend the interval between irrigations to let the turf and soil dry out. Water the turf in the morning, instead of in the evening, so the grass blades do not stay wet overnight.
Continue to mow on a regular basis. Match the mowing frequency with the growth rate of the grass. Return the clippings to the lawn as long as they don’t smother the grass.
When temperatures cool and the humidity drops, the brown patch fungus will go dormant and stop invading the grass plants. The turfgrass will recover on its own and the process can be enhanced by applying a lawn fertilizer when daytime temperatures drop below 70°F. After a few weeks of cool weather your lawn should look great.
Clark Throssell, Ph.D., is a turfgrass scientist and LebanonTurf staff member.