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.
Conditions 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
5. Night temperatures falling below 70.
6. Lawn thatch greater than 0.5″
7. Compacted soil
8. Absence of adequate soil biolife
In hot, humid weather the fungus Rhizoctonia solani becomes active. It grows well in thatch and soil. The survival structures germinate and produce grayish to brown mycelium that is capable of infecting the grass blades. Infection is most severe when the grass is succulent from nitrogen fertilization and when leaf surfaces remain wet from frequent irrigation or rain.
Brown patch disease cycle.
(image from The Compendium of Turfgrass Diseases, APS Press)
Treatment and Prevention
1. Reduce the presence of active fungi. Clean grass residue of mower after cutting affected areas on a sunlit hard surface such as a driveway. As the sun dries the residue it will kill the fungus and prevent transplanting the fungus to healthy areas,
2. Deter vigorous growth of a susceptible grass. Fast acting chemical fertilizers high in nitrogen cause a flush of succulent growth that is very susceptible to brown patch. Use only slow acting organic fertilizers.
3. Eliminate lawn thatch greater than 0.5″. Thatch is an excellent “home” for the fungus because of its hater holding properties.
4. Reduce compacted soil. Aeration facilitates surface drainage and allows air and nutrients to get to roots and soil biolife.
5. Make sure there is adequate soil biolife. Beneficial biolife (bacteria and enzymes) feed on harmful fungus, decompose thatch turning it into healthy lawn humus and transform nutrients and trace elements into nutrients for your lawn. I recommend Bio-enhanced liquid dethatcher.
6. Feed your soil biolife. One of the best biolife foods is molasses. Molasses has over 100 complex sugars that feed a significantly more diversity of microbes. I recommend Nature’s Magic (a combination of humic acid – sometimes called liquid humus and molasses supplemented with over 30 trace elements and plant hormones.
7. Refrain from using chemical fungicides. Although these kill the Brown Patch fungus, they also kill the biolife that will naturally eliminate them. Horticultural Cornmeal is a favorite food of a certain very friendly Good Fungus, called Trichoderma. This Fungus attacks several common Bad Fungi that attack Lawn grasses, specifically Sclerotinia (‘Dollar Spot’), Sclerotium (‘Southern Blight’ and other diseases), and Rhizoctonia (‘Brown Patch’). Note: horticultural cornmeal is not corn gluten meal. Corn gluten meal is an excellent pre-emergent weed controller but has no effect on fungi. Horticultural cornmeal is the organic fungus controller. When used at a rate of 10-20 pounds per 1,000 square feet every 90 days, corn meal will keep all (yes all) turf fungus at bay. If the fungus has already gotten a foothold, use it at 20 #/1,000 square feet.
8. Irrigate only when needed and then irrigate deeply (6-8″). Irrigate during the pre-dawn hours or early morning so surface water can evaporate before the afternoon day heat arrives. Never irrigate in the late afternoon or evening.