Brown patch disease occurs in all cool-season turf grass varieties. Severe outbreaks not only ruin the appearance of a lawn but make it thin, weak and susceptible to further disease. Catching brown patch early gives you the opportunity to properly manage the disease and prevent further harm to the turf.
Brown patch disease is caused by the fungus Rhizoctonia solani. It occurs often in ryegrass, tall fescue, creeping bentgrass and Kentucky bluegrass. The disease often occurs between July and September when the cool-season grass is at its weakest.
The main symptom is circular, brown patches. The brown patches are between 4 to 12 inches in diameter, says Purdue University. The leaf blades are brown within the patch while the perimeter of the circle is surrounded by a gray-white band when the patch is active. The band is caused by the moving fungus.
The fungus is at its strongest during the hot and humid summer months, says the University of Rhode Island, and grows especially well in grass that has a thick layer of thatch, a collection of dead plant particles. Grass that is moist from frequent rains is in high danger of becoming infected.
Do not overfertilize the lawn. Excessive amounts of nitrogen in the lawn cause lush growth that is susceptible to brown patch disease, says the University of Nebraska-Lincoln. Light, frequent fertilization prevents this. Water the turf properly as well. If the turf requires water, moisten to a depth of 6 inches early in the day so that the leaves do not stay wet.
Spray the lawn patch with fungicides to prevent the further spread of the disease. Fungicides are best applied during humid weather when a warm night is forecast. Apply and mix the fungicide according to the label instructions. Fungicide is normally not necessary for home lawns, as the turf will generally recover when proper conditions are provided or better weather arrives.