Rye grass is a non-spreading bunchgrass that germinates and grows quickly, providing early site coverage. Rye grass is added to seed mixtures because when it is planted alone it grows in tufts, resulting in bare spots. As a cool-season grass, it is used in the South to overseed a lawn to keep it green during the winter. The main problems with rye grass are caused by fungus.
Rye grass requires a soil pH between 5.5 and 8.0, according to “Lawn and Ground Covers,” by James Underwood Crockett and Time-Life Books. Ophiobolus patches are caused by a fungus, and although rye grass is less susceptible than other types of grass, some rye grass strains are still affected. Ophiobolus patches present as irregular-shaped, light red-brown patches on the lawn that eventually turning gray or yellow. To correct this condition, maintain proper pH and avoid using quick-release nitrogen fertilizer. Instead, add nitrogen by adding an acid-forming ammonium sulfate fertilizer to the grass.
Red thread disease is also caused by a fungus, identifiable by what looks like red threads on the top of the grass blades, according to Cornell University. Not all rye grass formulations are affected. The disease thrives in cool, damp weather in the spring and fall when puddles of water form on the grass. First, the blades of grass die and turn yellow, then the roots die and the yellow patches spread throughout the lawn. To avoid the disease, experts advise to keep the grass well fed in the spring and fall, provide good drainage, maintain the proper pH and avoid watering the lawn in evening.
Pythium blight, also called grease spot, is caused by a fungus that causes a white-cottony film to appear on the grass, followed by round, red-brown spots with greasy black borders. All types of grass in hot, humid conditions are susceptible to the disease, according to Richard L. Duble of the Texas Cooperative Extension. To avoid the disease, water grass only when needed and early in the day, improve the lawn's drainage, mow high and remove thatch to encourage root growth.