INFLUENCE OF CANOPY STRUCTURE ON TALL FESCUE CULTIVAR SUSCEPTIBILITY TO BROWN PATCH DISEASE

Tall fescue (Festuca aurundinacea) cultivars were evaluated under grow th chamber and field conditions for susceptibility to brown patch dise ase caused by Rhizoctonia solani. Percentage foliar necrosis varied am ong cultivars in growth chamber experiments. Kentucky-31 was the least susceptible cultivar (cv.), sustaining <25% necrosis 6 days after ino culation with the pathogen. Severity of necrosis in other cvs under th e same conditions was as high as 88%. Brown patch disease development in the field was lowest in cv. Kentucky-31 among nine cvs evaluated ov er two years. Average blight severity in cv. Kentucky-31 in 1991 was 3 4%, compared with 60% in the most susceptible cv., Trailblazer. Simila rly in 1992, cvs Kentucky-31 and Trailblazer had the lowest and highes t levels, respectively, of brown patch lesion development. Leaf blade density and verdure in the field varied among the cvs. Blade density a nd verdure correlated (r = 0.78 and 0.68, respectively; p < 0.05) with the extent of lesions measured in 1992, but were not related to mean blight severity measured in 1991. Field disease levels observed in bot h years had low correlations (r = 0.59; p = 0.10) with levels of necro sis measured in the growth chamber.