Tall fescue grass, according to the Alabama Cooperative Extension, is a cool-season bunching grass. Tall fescue has a high shade tolerance and grows green in the winter. Although mainly disease resistant when treated properly, tall fescue will fall victim to disease when weakened by excessive moisture or high heat conditions.
Brown patch is a disease caused by the fungus Rhizoctonia solani. Brown patch develops when night temperatures are higher than 60 degrees F, says North Carolina University, while low and high temperatures of 70 and 90 degrees makes the disease more severe. Brown patch causes circular brown patches that are anywhere from 1 to 3 feet in diameter. In fescue grass that is kept lawn, blades will wilt and die. Good management and selection of brown patch resistant tall fescue varieties will help prevent the disease.
Pythium blight appears as small circular, sunken patches up to 1 foot in diameter during humid weather. The patches are matted and have an orange or dark gray color, and are also greasy in appearance. 12 to 14 hours of continuous leaf wetness in combination with night temperatures exceeding 65 degrees F are the ideal conditions for the disease. A fungicide is the best form of pythium blight control.
Gray Leaf Spot
gray leaf spot is a disease that was once only found in St. Augustine grass but has since spread to tall fescue and ryegrass. Symptoms of gray leaf spot include small, round spots grayish brown spots on the leaves and leaf sheath. Spots increase in size, at which time the center of the spots turn to a dark gray and sometimes a yellow halo appears around the spot. Selecting resistant varieties, as well as caring for the grass properly will reduce the incidence of gray leaf spot.
Net blotch is a common disease of tall fescue grass, says the Alabama Cooperative Extension Service. Small brown spots appear along the leaf margin, caused by the fungus Drechslera dictyoides. Spots merge together over time, creating lines along the leaf that looks like a net. Growing disease resistant varieties and treating existing disease with fungicide is the best form of control.