The telltale sign of Leaf Spot is the purplish-brown to black-colored spots (or lesions) on the leaf blades and sheaths of your lawn. The tan centers of these spots become lighter as the lesions expand, developing a dark brown to black border. In some instances, the lesions will develop a yellow halo around the border and lower leaves eventually wilt and shrivel. If this lawn disease gets severe enough, Melting Out—the thinning of grass—can occur. Melting Out generally comes after leaf spots appear on cool-season grasses.
A Leaf Spot infection can occur only if all of the following conditions are present: 1. Pathogen: Bipolaris spp. or Drechslera spp. lawn fungi 2. Host: Bluegrasses, Bermudagrass, Fescues or Perennial Ryegrass 3. Environment: Moist to wet climates with temperatures ranging from 40°-80°F and soils with high nitrogen levels
Because you can't change your environment, the best way to control Leaf Spot is to create conditions that will foster a healthy lawn. Not only will this make your yard unfavorable for Leaf Spot growth, it will lower your risk of extensive damage should the lawn disease develop—plus you'll have the type of lawn you'll want to live on. For Leaf Spot control and lawn fungus treatment, TruGreen® recommends the following cultural control tips: • Increase the mowing height • Avoid excessive application of fertilizers with water-soluble nitrogen in the spring • Minimize the amount of shade, and increase air flow • Irrigate as infrequently as possible—when irrigation is performed, irrigate grass deeply