One of the most common diseases, seen in spring, is red thread. This disease is usually associated with perennial ryegrass, fine fescues, and Kentucky bluegrass. The fungus that causes Red Thread overwinters as dormant mycelium on dead leaves and stems of previously infected plants. It will become active during rainy periods in late spring and early summer.
Red thread disease tends to develop when air temperatures are 65° to 75°F, with prolonged periods of rainy or humid weather in late spring and early summer. Red thread frequently occurs with another disease called pink patch. Both diseases develop under the same environmental conditions and control measures are similar for both diseases.
Red thread disease symptoms appear as circular or irregularly shaped patches of blighted turf, typically with a red or pink cast. In the early stages of the disease, symptoms appear as small, blighted areas on leaves that can enlarge rapidly to cover most of the leaf surface. In the advanced stages, leaves become covered with bright red thread-like strands of fungal mycelium, 1⁄16 to 1⁄4 inch in length, at the tips of the affected leaves. Diseased plants eventually dry out and fade to a bleached straw color.
