Brown blight is a disease that occurs on Perennial Ryegrass during cool, wet, and cloudy periods in the spring or fall. Brown blight is a ‘Helminthosporium’ disease, which is a complex of diseases caused by fungi that produce large, cigar-shaped spores.
Symptoms of brown blight initially appear as small, brown, round or oval spots on the perennial ryegrass leaves. As the disease progresses, the lesions expand and become more numerous, causing a brown or yellowish brown dieback of entire leaves or plants. This foliar blight stage appears in irregular patterns, although certain ‘hot spots’ may be more severely damaged than others.
Brown blight is one of several Helminthosporium diseases which survive in thatch during periods that are unfavorable for disease development. These fungi are most active during periods of cool (60 to 65°F) and wet weather. Brown blight is most severe on turf that is growing slowly due to adverse weather conditions or improper management practices.
Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness that favor infection and disease development. Deficient or excessive nitrogen, excessive thatch, extended periods of leaf wetness, drought stress, and mowing heights that are too low or too high encourage the development of Helminthosporium diseases. Certain cultivars of turfgrasses are very susceptible to injury from Helminthosporium diseases while many of the newly released cultivars exhibit good resistance.