Dollar spot is a fungal disease that infects creeping bentgrass, Kentucky bluegrass, annual bluegrass, and fine-leaf fescues. Even Bermuda grass and zoysia grasses can become infected. The disease appears as roundish brown spots in the lawn. Initially, spots are the size of a silver dollar (hence, its name); later, they may be as large as 4 to 8 inches in diameter. You will not see larger ones unless spots merge. The affected area eventually turns straw-colored and appears sunken in the lawn.
A quick and rather good diagnostic guide involves the appearance of the leaf lesions. Look for these on plants at the edge of the sunken areas. The lesions girdle the blade, may be up to 1 inch long, and are usually bleached white to light tan, with a dark-brown, reddish brown, or purplish border. When dew is present on the blades of grass on overcast days or early in the morning, a white cobwebby growth of mycelia may be seen on infected plants.
This disease appears in warm (60 to 85°F), wet, and humid weather, especially in lawns that are low in nitrogen. Control measures include maintaining balanced fertility, avoiding late-afternoon or evening watering, providing good air circulation in the area by pruning surrounding plants, providing adequate surface drainage, mowing at the maximal height, and using resistant cultivars of grass. Chemical options can be used on a preventive basis but are generally used on golf courses. Refer to the Illinois Homeowners’ Guide to Pest Management Handbook or the Illinois Commercial Landscape & Turfgrass Pest Management Handbook for chemical options. Also, refer to Report on Plant Disease No. 407 for details on the disease, pathogen, and management options.