Brown spots in tall fescue grass is often caused by a fungal disease called brown patch. Unlike other types of lawn problems that result in grass browning, like pet urine, brown patch creates circular or spot-like patterns of discolored grass in the yard. In addition, brown patch typically occurs during hot and humid summer months. Gardeners may see brown spots appear in their lawn overnight. By using both cultural and chemical control methods, gardeners can rid tall fescue grass of brown patch.
Apply a fungicide that contains an active ingredient, such as chlorothalonil and mancozeb, every seven to 14 days. For long lasting treatment, use a fungicide that contains dicarboxamide or benzimidazole every 14 to 21 days. Dilute the fungicide in a tank according to the directions and spray on the tall fescue grass.
Water the lawn every three to four days in the morning to prevent excessive moisture loss. Give the tall fescue 1 inch of water to a depth of 3 to 4 inches. Dig a hole in the lawn after watering to ensure that the water has reached the root zone. Apply more water of the soil isn't moist.
Fertilize the lawn with 1/4 lb. of slow release nitrogen in the summer using a drop spreader. By applying a small amount of fertilizer in the summer along with a fungicide program, gardeners encourage healthy top growth. In September and November, fertilize the tall fescue with a fertilizer with an NPK amount of 16-4-8 at a rate of 1 lb. of nitrogen per 1,000 square feet. Water the lawn with 1 inch of water after applying the fertilizer.
Mow the tall fescue grass to 3 inches. Avoid taking off more than 1/3 of the grass blade at one time to prevent causing stress to the roots. To maintain 3 inches in height, mow when the lawn reaches 4 inches. Use a measuring stick to check.
Rake up grass clippings. The fungal diseases that cause brown patch survive on grass clippings and can spread to other parts of the yard.