This spring the Iowa State University Plant Disease Clinic received several samples of turfgrass with Ascochyta leaf blight. The disease can occur on many turfgrass species.
Look for large areas of straw-colored turfgrass. Individual blades usually die back from the tips and have a pinched appearance right above the green area of the leaf. Sometimes the infection can start in the center of the blade forming a straw colored band.
There are approximately 80 species of fungi in the genus Ascochyta that can cause Ascochyta leaf blight. They prefer humid, wet weather. Other factors, such as thick thatch, poor soil, over or under-fertilization, and dull mower blades can contribute to disease severity.
Maintaining a vigorous lawn is the best prevention against Ascochyta leaf spot. Core aerate in the spring or fall to reduce or prevent thatch build up. Keep mower blades sharp. Never remove more that 1/3 of the blade at one cutting. Mow when the grass is dry to avoid spreading spores. Use a balanced fertilization program. Fungicides are available, but won't have much affect without the cultural practices previously mentioned.
This article originally appeared in the July 12, 2002 issue, p. 95.