Read: How to spot Brown Patch
Brown Patch (also called Rhizoctonia blight) is a disease most common to Bermuda, Kentucky Bluegrass, Centipede Grass, Bentgrass, St. Augustine, and ryegrasses in regions with high humidity and/or shade. Brown patch commonly starts as a small spot and can quickly spread outwards in a circular or horseshoe pattern up to a couple of feet wide. Often times, while expanding outwards, the inside of the circle will recover, leaving the brown areas resembling a smoke-ring. Brown patch can temporarily harm a lawn's appearance and cause permanent loss of grass plants that are less than 1 year old.
Brown patch is a fungal disease that presents a serious threat to St. Augustine each spring and fall. With the onset of cooler temperatures, wet and overcast conditions, brown patch presents a challenge to St. Augustine lawns.
Conditions most favorable for brown patch development include (1) the presence of active fungi, (2) vigorous growth of a susceptible grass, (3) daytime temperatures ranging between 75 — 85, (4) the presence of free moisture on the foliage, and (5) night temperatures falling below 68.
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.
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.
The most common fungicides used on Brown Patch are: benomyl, chlorothalonil and Armada fungicide (a professionally applied product). Brown patch controls with fungicides containing thiophanate-methyl and/or chlorothalonil become ineffective as temperatures exceed 90°F. Other fungicides containing mancozeb, myclobutanil, propiconazole, quintozene, thiram, or triadimefon may also be used.