Usually caused by fungi, turfgrass diseases can at worst kill large areas of your lawn, and at the very least, cause unsightly patches in your grass. Many different turfgrass diseases exist, some of which are more common than others. The key to treating lawn diseases is properly diagnosing the infection. You also need to practice proper lawn care and, in cases of severe infections, apply a fungicide.
Dollar spot disease causes straw-colored, circular spots in turfgrasses that are only 1 to 2 inches in diameter. Caused by the fungus Sclerotinia homoeocarpa, dollar spot infects all types of turfgrasses, and it usually arises during extended wet periods or when there are low nitrogen levels in the soil. You can get rid of dollar spot disease in your lawn by applying an appropriate fungicide, as well as by properly watering, dethatching and fertilizing the lawn.
Brown patch disease, caused by the Rhizoctonia fungus, occurs most often from late April through October, when humidity levels are high, nighttime temperatures are warmer than 65 degrees Fahrenheit, the soil and grass blades are excessively wet, and nitrogen levels are high in the soil. Brown patch causes the leaf blades to turn straw-colored in large, irregularly circular patches of more than 4 inches in diameter. Control brown patch by reducing or stopping all nitrogen fertilizer applications, increasing the mowing height, watering earlier in the day and applying an appropriate fungicide.
Light-yellow flecks on the leaf blades that grow larger and elongate are signs of rusts, caused by the fungi species Puccinia and Uromyces. The yellow flecks develop into raised bumps on the grass blades, and then rupture and release yellowish-orange to reddish-brown spores. Rusts develop in early spring through mid-summer in shady, moist lawn areas when temperatures are 65 to 85 degrees Fahrenheit. Treat rust diseases by fertilizing your turfgrass with nitrogen, dethatching your lawn, watering the grass deeply, but infrequently, and applying a recommended fungicide.
Root Rot (Gaumannomyces graminis)
Root rot usually infects lawn areas with a soil pH of 6.5 or higher (alkaline) during excessively wet conditions, causing circular patches of wilted, brown or bronze-colored grass that are up to 2 or 3 feet in diameter. The infected grass appears as decayed, dark-brown roots. Treat root rot disease by applying an acidifying fertilizer, avoiding lime applications, dethatching, improving lawn drainage and applying a fungicide.
Caused by the mushroom-producing fungi Basidiomycetes, fairy ring infects turfgrasses most often during humid, moist and warm weather. Fairy ring causes rings or halos of dead, brown grass, inside and outside of which are spots of healthy grass. The rings may also have mushrooms growing along them. To treat fairy ring, you'll need to leach out the fungi by saturating the infected areas with water, directing the water away from the grass roots, as well as apply a recommended fungicide.
Gray Leaf Spot
Gray leaf spot, caused by the fungus Pyricularia grisea, occurs in warm, humid conditions, and when there are high nitrogen levels in the soil. You'll see small brown spots on the leaves and stems of the turfgrass, expanding rapidly to about ¼-inch long, and turning bluish-gray and oval or elongated. The lesions turn tan or gray with indented centers and irregular edges that can be yellow, purple or brown. Reduce the amount of nitrogen that you feed your lawn during mid-summer, water the lawn deeply but infrequently, dethatch the lawn, and apply an appropriate fungicide to get rid of gray leaf spot disease.
Other Turfgrass Diseases
Some other less-common turfgrass diseases include fading out, Pythium, Helminthosporium leaf spot and slime mold. Fading out and Helminthosporium leaf spot both attack excessively wet turfgrasses when soil potassium levels are low and nitrogen levels are high. Helminthosporium leaf spot causes small dark streaks or spots on the turfgrass blades, while fading out causes spots on the blades that vary in color and appearance, depending on the grass species. Pythium also occurs in wet weather, but it causes small irregular, dead spots in the lawn that appear to be oily or water-soaked and matted. You'll also see white cottony mycelia on the grass. You can control these turfgrass diseases by applying the appropriate fungicide. Slime mold, another turfgrass disease, is generally harmless and will resolve itself when drier weather returns.