Red Thread on Ryegrass: The Disease of of Spring

Red thread (casual agent: Laetiseria fuciformis) is a serious disease of cool season turfgrasses in the spring. It is especially severe on perennial ryegrass and slow growing Kentucky bluegrass. Symptoms usually appear as small circular to irregular shaped patches. The protruding red threads or sclerotia from the leaf blades are diagnostic keys to this disease. In some instances the mass of mycelium may be confused with Microdochium patch (casual agent: Microdochium nivale).   The confusion occurs on perennial ryegrass this time of the year. Cultural control practices include increasing the amount of nitrogen to the turf. This practice is effective on Kentucky bluegrass and to a lesser extent on perennial ryegrass. Keep the mower blade sharp and try to avoid mowing when the turf is moist. Also avoid overwatering in the late afternoons or early evenings. Watering at this time will promote disease development.   If red thread becomes severe enough fungicide applications may be warranted.