Rye Grass and Fungus

Red Thread

• Red thread is a fungal disease that occurs during cool moist weather conditions, according to North Dakota State University. When rye grass first contracts red thread, grass blades take on a bleached-out appearance. As the disease progresses, grass blades turn pinkish to whitish in color. A moderate infection may mean a few small patches of rye grass has been infected, but a severe bout of red thread can damage several feet of the yard. If closely examined, small tiny red fungal threads can be seen. Treat the rye grass with fertilizer to encourage healthy growth and water deeply.

Brown Patch

• Brown patch or rhizoctonia blight typically occurs during hot weather. Gardeners may see discolored patches of rye grass ranging between 1 and 3 feet in diameter, according to North Dakota State University. During humid weather, patches appear to have a dark gray or dark purple ring. Cultural control management options include reducing nitrogen applications and dethatching your rye grass if the thatch layer is more than 1/2 inch. If cultural measures have little effect on the spread of brown patch, treat the lawn with a fungicide.

Rust

• Humid warm weather favors the spread of rust disease. Rust is seen on lawns when daytime temperatures are between 85 and 95 degrees Fahrenheit and nighttime temperatures are between 70 and 75 degrees Fahrenheit, according to North Dakota State University. Infected rye grass takes on a red to yellowish appearance. In fact, gardeners may see an orange dust blow up from their lawns when mowing infected areas. Control your rust problem by deeply watering the lawn and providing fertilizer.

Pythium Blight

• Pythium blight infects rye grass lawns during hot weather. Greasy-looking spots may start to appear in the morning in infected areas. As the disease progresses, these spots die out. This fungal disease easily spreads through mowing, foot traffic and water runoff. Gardeners contribute to the disease by watering their rye grass lawn late in the evening. Wet blades and cool nighttime air worsen symptoms of pythium blight. Spread may be stopped if watering occurs in the morning or nitrogen is not given to the lawn during hot temperatures.