Rust is a fungal disease of tall fescue that causes the grass to take on a yellow appearance. The development of the fungi is favored by cloudy and cool weather.
Rust disease starts with the appearance small, yellow spots on the grass blades. As disease progresses, the spots enlarge and merge to give the grass an overall yellow look. The yellow spots also become raised and filled with yellow spores.
Keep grass in good health with adequate fertilization and irrigation to minimize risk of disease. Do not water lawns during late evenings as wet blades favor disease development. Do not move mowing equipment to healthy grass areas without proper washing. Cultural management is often enough to contain disease without the use of fungicides.