The extension office has recently received numerous phone calls from homeowners concerned about mysterious brown circular patches that have suddenly appeared on their lawns. The cause may be the fungal disease brown patch, which can destroy the beauty of a lawn.
It occurs when certain environmental and cultural conditions are present and the turfgrass is weak making it susceptible to the disease. Brown patch affects all types of turfgrasses and is the most common lawn disease. The disease is more prevalent on cool season grasses, such as tall fescue, in the summer months and warm season turf, such as bermuda and zoysia, during the spring and fall transition periods.
The symptoms of brown patch are thinned patches of light brown grass surrounded by a smokey-gray coloring. They are roughly circular in shape ranging in size from a few inches to several feet in diameter. The grass blades of the cool-season turf have small irregular tan leaf spots with dark-brown borders.
Warm-season grasses with this disease usually lack observable leaf spots, but have rotted leaf sheaths near the soil surface. In the early morning hours when the weather is warm and humid, white fungal webs at the edge of the dead grass patch may be visible. The grass may recover in a few weeks, especially if the disease attacks only the blades and the grass is in good health. However, severe infections on weakened turfgrasses during favorable environmental conditions can potentially destroy the crowns of the grass leading to death.
Nitrogen fertility has an important influence on the development of the disease.
High nitrogen levels promote the growth of soft, succulent grass blades that are more susceptible to the fungus. Avoid multiple applications of high nitrogen fertilizers to turfgrasses. The disease thrives on high humidity and temperatures above 80 degrees during the day and 60 degrees at night. On lawns where the foliage stays wet more than 10 hours a day for several consecutive days, brown patch can be more of a problem. Irrigate infrequently and let the water penetrate deeply, 4 to 6 inches. Apply the water early in the morning so the grass will dry out before the evening. Make sure the lawn has adequate drainage.
Turfgrasses with heavy thatch accumulations are more vulnerable to the disease. Periodic mechanical dethatching or core aerification is needed to reduce thatch levels. Mowing the turf below the recommended height can increase the lawn’s susceptibility to the disease. Also, make sure the mower blade is sharp prior to usage. Dull mower blades shred the ends of the grass blades which increases their likelihood of infection.
Using fungicides to control brown patch is difficult, but regular applications offer some level of protection. These chemicals suppress the development and spread of the disease, but do not reverse the already visible damage. Start applying them when symptoms are first observed and continue to apply them at the recommended label intervals until the disease is controlled. Use fungicides such as Bayer Advanced Lawn Fungus Control, Spectracide Immunox, Scotts Lawn Fungus Control and other ones labeled for controlling brown patch. As with any chemical pesticide, please follow all label directions and safety precautions.
Although chemical applications may help to suppress the spread of the disease, the control is only temporary. Long term control requires altering the cultural conditions that favor its development.
Timothy Daly is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or firstname.lastname@example.org.