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DALY: The cause of brown patches on your lawn

Many area homeowners are concerned about mysterious brown circular patches that have suddenly appeared on their lawns. Frequently the cause is the fungal disease brown patch which can quickly destroy the beauty of a lawn. It occurs when certain environmental and cultural conditions are present and the turfgrass is weak increasing its susceptibility.

Brown patch affects all types of turfgrasses and is the most common lawn disease. It is more prevalent on cool season grasses, such as tall fescue, during the summer months and on warm season turf, such as bermudagrass and zoysiagrass, during the spring and fall months. However, the disease can occur throughout the growing season.

The symptoms of brown patch on cool season grasses are thinning patches of light brown grass surrounded by a smokey-gray coloring. The patches 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 lesions with dark-brown borders. Infested warm-season grasses usually lack observable lesions, but have rotted leaf sheaths near the soil surface. The grass may recover in a few weeks, especially if the grass is in good health. However, severe infections on weakened turfgrasses during favorable environmental conditions can potentially destroy the crowns of the grass causing death. The fungus thrives under certain cultural conditions. Excessive amounts of high nitrogen fertilizer promote the growth of soft, succulent grass blades that are more susceptible to the fungus. Avoid or limit the applications of high nitrogen fertilizer to turfgrasses, especially during periods when the grass is most susceptible.

The disease is most active with high humidity and temperatures over 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. Apply the water early in the morning so the grass will dry out before evening.

Make sure the lawn has adequate drainage. Turfgrasses with heavy thatch accumulations are more vulnerable to the fungus. 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, the mower blade should be sharpened before using it. Dull mower blades shred the ends of the grass blades increasing the likelihood of infection.

Using fungicides to control brown patch is difficult, but they do offer some level of protection. These chemicals suppress the development and spread of the disease, but they do not reverse the already visible damage. Use fungicides labeled for controlling brown patch on turfgrasses and start applying them when symptoms are first observed. Continue applications at the recommended label intervals until the disease is controlled.

As with any chemical pesticide, 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 tdaly@uga.edu.