Purple Fungus on Fescue Grass

Leaf Spot

• Leaf spot is caused by Bipolaris sorokiniana fungal spores, according to North Dakota State University. These fungal spores survive in thatch layers and turf debris. When warm summer temperatures favor fungal spore germination, the disease attacks grass' blade and root systems. Grass blades exhibit spots with tan centers and purplish-red to purplish tan borders. Eventually, the disease kills the blade tips and moves into the roots, which is referred to melting out, according to the University of Rhode Island.

Melting Out

• Melting out is actually caused by different fungal spores called Drechslera poae, according to North Dakota State University. Melting out causes large areas of fescue grass to die out. You may see an irregular patchwork of dead fescue grass across your lawn, according to North Dakota State University. This disease is hard to stop. Gardeners should employ both cultural and chemical control methods to control leaf spot before it turns into melting out. Once the lawn exhibits signs of melting out, fungicide applications do little to help, according to the University of Rhode Island.

Treatment

• Treat leaf spot with fungicide every five to 10 days, as suggested by the University of Rhode Island. The frequency depends on how often you mow and the amount of rainfall your fescue lawn receives. In addition, avoid applying fungicides to a water-stressed fescue lawn. Severely damaged areas may need reseeding once the disease is under control. Dead grass in the yard encourages weed growth.

Prevention

• Removing a thick thatch layer removes some fungal spores, improves air circulation, prevents grass saturation and reduces the risk of leaf spot. Check the thatch build up in your fescue lawn by cutting out a 2-inch wedge of turfgrass. Measure the thatch accumulation. If the thatch layer is more than 1/2 inch, dethatch the lawn with a power dethatcher or a rake. Dethatching your fescue lawn in the fall when the grass is actively, growing prevents injury.