Most resources indicate that Ascochyta leaf blight is a minor disease because injury is usually temporary, and does not result in turf loss. Kentucky bluegrass is most commonly affected, but infection of other cool-season grasses is also possible.
Symptoms. Ascochyta may appear in isolated spots, or as large patches of straw-colored turf (similar to drought stress, but soil will likely be moist). Symptoms commonly appear following wet weather from late spring to summer, but infection may occur all season. Infections may also appear uniform and diffuse. Individual leaves bleach from tips, and sometimes have dark brown elliptical lesions with dark fruiting bodies called pycnidia.
Management. Disease development is most common in continuously wet turf areas, so irrigation management is most important to limit injury. Irrigate deeply and infrequently, and only early in the morning to limit the duration of leaf wetness. Early morning irrigation has the added benefit of knocking dew from leaves, further reducing the period of leaf wetness. Frequent mowing, especially when turf is wet or with a dull blade increases severity. Mow when leaves are dry. Most sources indicate that fungicides are not necessary unless development is severe, and that broad-spectrum active ingredients will protect turf. We have an outbreak of Ascochyta leaf blight on a perennial ryegrass fairway on campus, and haven’t yet seen benefit from applications of a number of different fungicides. Knowledge of effective fungicides in currently limited.
Bottom line. Ascochyta leaf blight may be confused with injury from drought stress, dollar spot, etc. Excessive, improperly timed irrigation and mowing increase severity. Unfortunately, knowledge of fungicide efficacy for this disease is currently limited, and the best way to prevent disease is with sound turf management.-Cole Thompson, Asst. Prof. & Extension Integrated Turfgrass Management Specialist, email@example.com