Tall fescue canopy density effects on brown patch disease

Canopy density was investigated as a factor determining the severity of brown patch disease, caused by Rhizoctonia solani, in the field. In two separate experiments, tall fescue (Festuca arundinacea) cv. Fawn was seeded at 10 to 50 g/m² to create canopies with different levels of blade density (i.e., numbers of leaf blades per unit area) and verdure. Brown patch lesion development was more severe at the 50-g/m² seeding rate than at 10 g/m² in both experiments. Six cultivars of tall fescue, representing combinations of susceptibility (as determined in a growth chamber) and stature (tall, medium, or dwarf), were evaluated in the field for brown patch disease severity and canopy density. Disease severity measured over 2 years was highly correlated with blade density and verdure, but was not related to cultivar susceptibility. The tall cultivars produced the least dense canopies and sustained the least amount of disease. The medium and dwarf groups, however, could not be distinguished on the basis of canopy density or response to brown patch disease. These results show that canopy density directly affects brown patch disease severity under field conditions and is, in part, related to a cultivar's stature.