Disease Invades NW Lawns

Red Thread is especially prevalent during the spring and autumn months on slow-growing, nitrogen deficient turf. It may cause severe damage to bluegrass, fescue, ryegrass and bent- grass species in humid and cool temperate regions of the world.

Diagnosis: Circular or irregularly shaped, small to large patches of infected grass become water-soaked and die rapidly. The tan color of dead leaves may be the first symptom observed. Dead leaves are generally interspersed among unin- fected leaves, which gives an overall diffuse, scorched, or ragged appearance to the patch. The patches may be widely scattered or close together and may join together to form large areas of infected turf.

Inspection of individual plants reveals that only the foliage is infected, and death usually proceeds from the leaf tip downward. When the air is saturated with moisture, the pathogen produces colorful mycelial structures that are of diagnostic value. Pink to pale red or orange fungal growths, called “red threads”, may extend up to 10 mm beyond the end of the leaf tip. Pink cottony flocks of mycelium up to 10 mm in diameter may also be produced. When the red threads or flocks are present, following humid weather, the patches of blighted grass take on a reddish cast that is easily detected.

Control: Based on soil reports, it is essential to maintain adequate and balanced soil fertility. Applications of nitrogen fertilizer are particularly helpful in reducing disease severity, but excessive rates of fertilizer must be avoided. The soil pH should be in the range recommended for growth of the turfgrass species in question (generally 6.5 to 7.0). Water as needed to prevent drought stress in the turf. Water should be applied thoroughly (deeply), as infrequently as possible, and early in the day. Avoid frequent sprinkling in the late afternoon; this encourages longer periods of leaf wetness.

Selectively prune trees and shrubs, or arrange the landscape design to increase light penetration and air movement over turf. Collecting turfgrass clippings during periods when grass is growing slowly may reduce the number of fungal threads that are incorporated back into the turf. Cultivars of the major turfgrass species vary as to susceptibility.
Note: Red Thread inform- ation provided courtesy of OSU Department of Horticulture.