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Brown patches on lawns result of fungal diseases

Many homeowners have observed brown circular patches on their lawns. The cause is often a fungal disease called brown patch (or large patch on warm season turf), and it can quickly destroy the beauty of a lawn. All types of turf grasses are affected by this disease.

The symptoms of brown patch causes thinned patches of light brown grass roughly circular in shape. These areas range in diameter from a few inches to several feet. The grass in the center of the patch will sometimes recover, resulting in a doughnut-shaped pattern. Upon closer inspection, the cool-season grass blades show small, irregular, tan leaf spots with dark-brown borders.

Warm-season grasses with this disease seldom have leaf spots but will have rotted leaf sheaths near the soil surface. In the early morning when the weather is hot and humid a smoky gray can be observed around the areas that are brown and diseased with brown patch, where as with the large patch on warm season turf the edges can have an orange color appearance.

Brown patch has individual leaves with lesions that develop with tan centers and dark brown to black margins. In large patch, the individual leaves have water-soaked, reddish-brown or black lesions with dieback from the leaf tip toward the base occurring. Both diseases prefer high humidity and warm temperatures over 80 degrees during the day and over 60 degrees at night.

In lawns where the foliage stays wet for several hours a day for several days in a row, brown patch can be more of a problem. Brown patch affects cool season turf more so in the summer months and large patch affects warm season in the spring and fall. Cutting the grass at a lower height than the recommended amount makes it more susceptible to the disease.

The best way of to control the disease is to use cultural lawn care practices, which are much easier and less costly than using chemical fungicides. Avoid applying fertilizers high in nitrogen to cool season grasses in late spring and summer, and to warm season grasses mid to late fall.

The fungus prefers grass with lush, new growth that results from too much nitrogen. Have the soil tested to determine fertility levels, and add lime if the pH is less than 6.5. Irrigate infrequently and let the water penetrate deeply 4 to 6 inches. Do the watering early in the morning so the grass will be drier during the evening hours. Keep lawns mowed at the recommended height, and prevent thatch buildup. Make sure the mower blade is sharp before use. Good drainage also reduces the susceptibility of the grass to brown patch.

Using fungicides to control brown patch and large patch is difficult but regular applications can reduce the spread and development of the infection. Start applying the fungicides when symptoms are first observed, and continue to apply at the recommended label intervals until the disease is controlled.

Usually only two or three applications are necessary to control the disease. For chemical control of brown patch on either cool- or warm-season grasses is to begin fungicide applications when night time low temperatures reach 70 degrees once every 14 days. Fungicides such as Captan, Maneb, Mancozeb, Myclobutanil and others are the recommended ones for controlling brown patch.

You can obtain more information on these chemicals and their usage by going to the 2007 Georgia Pest Management handbook at: http://www.ent.uga.edu/pmh/. For more information and consultation on these turf diseases or any other topic of concern, please contact the Gwinnett County Extension Office.

Timothy Daly is an Agricultural and Natural Resource Agent with Gwinnett County Extension. He can be contacted at 678-377-4010 or timothy.daly@gwinnettcounty.com