In the U.S. Pacific Northwest, the most significant diseases affecting seed production of tall fescue are fungal diseases, including stem rust caused by Puccinia graminis subsp. graminicola, and blind seed caused by Gloeotinia temulenta. Stem rust is an especially destructive foliar disease with potential for significant yield reductions. Fungicides are required for rust control. Blind seed is a disease of the developing seed, characterized by reduced seed germination. During the 1940s, blind seed caused devastating reductions in seed germination and threatened the grass seed production industry in the Willamette Valley (Hardison, 1962a).
By the late 1940s, postharvest field burning (see Chapter 18) was established as an effective control for blind seed. By the 1950s, field burning was generally accepted as a postharvest management practice for control of blind seed, other diseases, weeds, and as a means of straw residue removal. Field burning remained an important component of pest management in grass seed production in Oregon until legislation in 1991 limited acreage burned to 16,187 ha annually for grasses grown for seed in the Willamette Valley. Fortunately, there has not been a widespread resurgence of blind seed disease, but blind seed has caused significant reductions in germination in some fields of early maturing cultivars of tall fescue.
Other fungal diseases of tall fescue that are important but generally less destructive than rust or blind seed include Fusarium head blight, caused by Fusarium spp.; ergot, caused by Claviceps purpurea; and leaf spotting diseases, caused by species of Cercosporidium, Dreschlera, Rhynchosporium, and Septoria. Leaf spotting fungi are most active under cool, rainy conditions during fall and spring. In addition, damage to seed stalks from insects (see Chapter 9) or fungi can result in death and subsequent bleached or silvery-white appearance of the seed heads, a condition commonly referred to as silver top.
Disease control recommendations, including registered fungicides and application rates, for specific diseases in the Pacific Northwest are available at http://plant-disease.ippc.orst.edu (verified 11 May 2009). Although many other pathogens can infect tall fescue (Farr et al., 1989; Smith et al., 1989; Sprague, 1950) (see Chapter 8), they have not been found to be a problem in tall fescue seed production in the Pacific Northwest.