Brown Patch, which is also known as large patch, is a common soil-borne fungus that attacks a variety of plants including almost all turfgrasses. It is most common to Bermuda, Kentucky Bluegrass, Centipede Grass, Bentgrass, St. Augustine, and ryegrasses in regions with high humidity and/or shade. Tall fescue is also prone to the development of Brown Patch.
Brown patch commonly starts as a small spot that can quickly enlarge. As the disease progresses and becomes larger, it will take on a circular, or sometimes a horseshoe shape, that could be several feet across or larger. As the infected area becomes larger, the initially infected area begins to recover, creating a brown circular pattern in the lawn.
Conditions most favorable for brown patch development include the presence of active fungi responsible for the disease coinciding with a seasonal time when the susceptible grass is aggressively growing combined with a climate where daytime temperatures range between 75 — 85 degrees and night-time temperatures hover above 65. Poor surface and subsurface drainage combined with excessive fertilization (nitrogen) are both factors that greatly increase the intensity of this disease.
On warm season turf grasses, the disease is characterized by at least two different types of symptoms. The most common is a circular pattern of brown grass with a yellowish ring (smoke ring) of wilted grass on the perimeter of the diseased area. The leaves can be easily pulled from the stolons with the smoke ring because the fungus destroys the tissue at the base of the leaf. Symptoms first appear as small circular patches of water-soaked, dark grass that soon wilt and turn light brown. Stolons often remain green as the disease develops, the circular patches enlarge, smoke-rings become apparent and new green leaves may emerge in the center of the circular areas.
When environmental conditions are favorable, brown patch is likely to develop on susceptible turf grasses. The severity of the disease can be somewhat controlled by following a strict fertilization schedule that only apply the proper amount of nitrogen and trace elements during the ideal times; by watering early in the morning to remove dew and all the grass to dry quickly; mow grass a little taller with a sharp mower blade, and when possible , by bagging the lawn clippings during likely periods of disease activity. Fungicide applications are most effective when used as a preventative before the disease has become established in the lawn.
Since brown patch typically only kills the leaf, lawns attacked by brown patch will usually return when conditions improve as long as secondary problems do not take advantage of the turfgrass in its weakened state.
The best prevention for brown patch is to aerate often, reduce shade to effected areas, and follow a fertilization schedule to help prevent fertilization with excess amounts of nitrogen. Avoid irrigating late in the day. Do not over-fertilize.
The most common fungicides used on Brown Patch are: benomyl, and chlorothalonil. The brown patch fungus will survive in thatch and turf debris between periods of activity. Chemical controls are available, but should only be applied by licensed applicators. Contact your local lawn care provider for additional information.
Brown patch symptoms can vary depending on the grass variety, the soil as well as climate. Once it takes hold, the disease can spread quickly and begins to appear with 24 - 36 hours after infection. In the early morning on close cut turfgrasses, a dark smoky ring may appear at the periphery of the patch. This smoky ring transforms as the day progresses into a uniformly light brown or straw color.
Typically, brown patch causes rings or patches of blighted grass that measure from 5" to more than 10' in diameter. It also causes leaf spots and thin rings with brown borders around the diseased patches. Under close examination of the blades, irregular spots may be noticed that is bordered by a darker margin.
After the leaves die in the blighted area, new leaves can emerge from the surviving crowns. On wide-bladed species, leaf lesions develop with tan centers and dark brown to black margins.
Brown patch favors high humidity and temperatures over 85 degrees during the day and not below 65 at night. On warm season grasses, this disease can be very active in the spring and fall. It also occurs in areas that receive more than 10 hours a day of wetness for consecutive days.
Brown patch infestation is more severe when the grass is cut to a height less than the optimum for the variety of grass.