Brown Lawn Fungus

Identification

• Brown patch is a common fungal disease that affects all cool-season grasses including fescues, ryegrasses, bluegrasses and bentgrass. The disease is caused by Rhizoctonia solani and is mostly seen on lawns between May and September. Brown patch disease is also referred to as rhizoctonia blight.

Favorable Conditions

• Being a summer disease, the fungus causing brown patch becomes active during extended hot and humid weather with nighttime temperatures of 60 degrees Fahrenheit or more. The optimal temperatures favoring disease range between 70 and 90 degrees F. Grass that stays consistently wet for 10 to 12 hours is more prone to the infection. Other factors favoring an outbreak include poor air ventilation, over irrigation and poor soil drainage. Excessive use of nitrogen and inadequate levels of potassium and phosphorus also make lawns prone to infection.

Symptoms

• The disease starts with the appearance of 4- to 12-inch-diameter olive green patches on the grass that gradually turn brown. There is a grayish white border, often referred to as a smoke ring, around the patches. Inspection of individual grass blades reveals brown lesions. These lesions are most pronounced on tall fescue lawns. The fungus survives in the soil and thatch in the form of resting bodies or sclerotia and becomes active as soon as the weather becomes favorable.

Control

• Prevent chances of infection by avoiding excessive use of nitrogen fertilizer. Do not fertilize cool-season grasses in spring or summer but, rather, in fall and early winter. Mow the lawn at a 2 1/2-inch height and more often using a sharp blade. Water deeply to a depth of at least 4 inches rather than light, frequent watering. The use of fungicides is not recommended in established lawns, cites University of Kentucky Extension.