How Can I Prevent Fungal Diseases On My Lawn This Year?

Did you have problems with brown patch disease in previous years?

Did you have problems with dollar spot disease in previous years?

Did you have problems with fairy ring disease in previous years?

Did you have problems with fusarium blight disease in previous years?

Did you have problems with Pythium blight disease in previous years?

Did you have problems with red thread disease in previous years?

Did you have problems with rust disease in previous years?

Did you have problems with snow mold disease in previous years?

Brown patch disease (caused by Rhizoctonia solani) shows up as areas where the grass darkens and then browns and dies. Its favorite hosts are grasses that have been given excessive amounts of nitrogen fertilizer. To prevent brown patch, cut back on fertilizers containing nitrogen and check the drainage in the lawn. If you can improve it by making a ditch, do so. Otherwise, rely on additions of compost to help build a soil structure that allows fast drainage.

Dollar spot disease (caused by Sclerotinia homeocarpa) causes round, white spots in the lawn, about the size of a silver dollar. The margins of the spot are sometimes a dark brown, but this is not always the case. Prevent dollar spot by keeping the grass moist and by making sure that nitrogen levels are adequate. The disease is most likely to strike when both water and nitrogen levels are low. Mow high to cut off the infected areas and bag the cuttings so you can remove them.

The first sign that fairy ring (caused by Marasmius oreades) has infected your grass is a circle of dark green grass. Later, the mushrooms grow on the circumference of the affected area giving it a ring-like appearance. Reduce thatch by mowing the grass with a vertical mower and by aerating the lawn. Remove tree stumps and roots to reduce the amount of organic matter on which the fungus feeds. Add a fine layer of high-quality sand on top of the lawn. This dilutes the amount of organic matter and provides a substrate for turfgrass root growth.

Fusarium blight (caused by Fusarium tricinctum) shows itself as small, discolored patches in the lawn, only 2 to 6 inches wide, that look reddish-brown. As the disease progresses, the spots turn yellow. If you examine the rotting crowns of the plants, you may see the pink fungal body. Prevent fusarium blight by keeping nutrient levels balanced. Don't add nitrogen-containing fertilizers after early spring. Water early in the day to reduce nighttime humidity levels. Mow high to avoid stressing the plants and remove the clippings rather than leaving them on the grass. If your grass has a thatch problem, remove what you can and aerate to discourage it.

Pythium blight (caused by Pythium aphanidermatum) looks like patches of rotting grass. It spreads quickly, so prevention is the best recourse. Watch pH and calcium levels in the soil and add lime whenever there is a deficiency of calcium or the pH falls below 6.0. Water only in the morning and don’t let thatch accumulate.

Red thread (caused by Laetisaria fuciforme) appears as red threads of the fungus growing beyond the leaf tips. Mowing with a bagger attached often keeps the disease from spreading extensively. Preventive treatments include keeping nitrogen levels adequate for good growth and watering deeply and frequently without keeping the soil saturated.

Rust (caused by Puccinia spp.) can strike in any part of the country and at any time of the year. The symptoms of this disease are rusty- to yellow-looking patches on individual leaf blades. You can rub off the colored spores if you try. The disease is most common on damp areas of lawn in the shade. Water only in the morning so the grass can dry by nightfall. If drainage is a problem, try to improve it, and keep grass growing well with adequate, but not excessive, nutrient levels.

The first symptoms of snow mold (caused by Fusarium nivale) are 1- to 2- inch wide circles of grass with dark-colored, wet-looking spots. As the disease progresses, the spots change to a tan and then a white color. It looks pink in bright light. Prevent this disease by fertilizing and liming only in the early spring—never in the fall. Don't let thatch build up and improve drainage if it’s a problem.

The leaf spot diseases that affect grass are similar to the leaf spot diseases that attack vegetable crops. Several different organisms cause several different leaf spot diseases. Mow high and remove clippings and make certain to keep thatch from accumulating. Depending on the type of leaf spot several kinds of grass are resistant to these diseases.