Rhizoctonia (or Large Brown Patch) is present in most types of soils. This soilborne fungus attacks several plant types including grasses, vegetables, flowers, and even field crops. It usually appears in highly fertilized soils of plants that are covered with a film of moisture for at least 12 hours each day. Other conditions that promote Rhizoctonia growth are a temperature of 70-95 F for several hours each day, and the infection of the fungus from contaminated soil.Bluegrass Rhizoctonia solani

When turfgrass is infected with Rhizoctonia, it is hard to identify because the symptoms are similar to other lawn diseases. It usually takes a microscope for someone to accurately identify its presence, although some readily seen symptoms may be present. In bentgrass turf, Rhizoctonia is roughly circular, with light brown patches ranging from a few inches to 2-3 feet in diameter. The grass blades often appear dark and water-soaked, but they soon dry out. The dried blades of grass remain upright, which isn't similar to under-watered grass. With Rhizoctonia, only the leaf blades are usually affected, although the new grass growing from the roots will be much thinner.

To determine how advanced the disease is, look for a grayish "smoke ring". This ring is roughly 1.5 inches wide and is composed of wilted grass blades. Although light infections often clear up in 2 or 3 weeks, severe infestations of Rhizoctonia cause greater damage to your lawn. The roots, crown, and rhizomes of your grass will rot away.

To prevent and control Rhizoctonia, avoid overferilization - especially in hot seasons. Stick to fertilizers with a proper balance of Nitrogen, Phosphorus, and Potassium. The grass should get the chance to dry after being watered or covered in dew. When thatch exceeds half an inch thick, remove the excess with a rake or a vertical mower. You can also spray a preventive fungicide to protect your lawn from Rhizoctonia. Use minimum doses for prevention, and use the full dose for curing an already infected lawn.