All of the leaf spot diseases are favored by prolonged cool and wet conditions. The effect of leaf spot diseases on seed yields in tall fescue is not established, but in most years they likely do not contribute to significant reductions in yield. The diseases can be controlled by fungicides. Sources of additional information on leaf spot diseases of tall fescue include Smiley et al. (1993), Smith et al. (1989), and Sprague (1950).
Dreschlera and Bipolaris species cause reddish brown spots or streaks and leaf die-back. Longitudinal and horizontal streaks on the leaves produce a net-like appearance. The disease is commonly referred to as net blotch. The fungus survives as conidia and as dormant mycelia in infected tissue. Dreschlera also can cause crown or root diseases, although these have not been reported as causing problems in tall fescue seed production.
Rhynchosporium spp. cause leaf spotting, leaf die-back, or scald. Conidia are produced during cool, wet conditions and are disseminated by wind and rain splashing to healthy leaves. Rhynchosporium spores germinate and directly penetrate the leaf surface. The fungus proliferates within the leaf tissue and produces conidia on the leaf surface above lesions (Fernandez and Welty, 1991). The fungus survives as dormant mycelia in living or dead plant tissue.
Septoria causes grayish leaf spots. Conidia are produced in pycnidia, which appear as tiny black dots in the center of the lesions. Septoria survives as mycelia or pycnidia in infected tissue.
Cercosporidium graminis (Fuckel) Deighton is a common, widespread fungus with a host range that includes all cool-season turf and forage grasses. It is a common disease in the spring in the Willamette Valley on grasses grown for seed. Symptoms include elongated, brown to gray lesions. Cercosporidium graminis is favored by conditions that are cooler and wetter than normal (Welty, 1991).