INTERACTIONS AMONG MOWING HEIGHT, NITROGEN FERTILITY, AND CULTIVAR AFFECT THE SEVERITY OF RHIZOCTONIA BLIGHT OF TALL FESCUE

The effects of three mowing heights (3.8, 6.4, and 8.9 cm) and three nitrogen fertility regimes (0, 24.4, and 48.8 kg N per ha per month) were assessed on epidemics of Rhizoctonia blight in four cultivars and one cultivar blend of tall fescue in 1993 and 1994. Significant differences in disease severity were observed among mowing heights, fertility regimes, and cultivars or blend in each year. In addition, significant cultivar x mowing height interactions were detected in both years, and significant cultivar x fertility interactions occurred in 1993. The cvs. Mojave and Rebel II exhibited significantly more disease than the other cultivars or blend late in the 1993 study. Analysis of interactions revealed that disease was significantly greater on these cultivars than on others at fertility regimes of 0.0 and 24.4 kg N per ha, and at mowing heights of 3.8 and 6.4 cm. In 1994, Mojave again exhibited significantly more disease than the other cultivars or blend at the 3.8 cm mowing height near the peak of the epidemic, and Rebel II was the only cultivar that displayed significantly more disease at the 6.4 cm height than at the other heights tested. Across cultivars, severity of Rhizoctonia blight was significantly greater at the 8.9 cm mowing height than at the 3.8 cm height during epidemic peaks in 1993. The opposite was observed in 1994. Each cultivar or blend exhibited significantly more disease in fertilized than in nonfertilized plots by at least one of the dates on which significant cultivar x fertility interactions were detected in 1993. In 1994, data from nonfertilized plots was withheld from analysis due to an epidemic of white blight that interfered with assessment of Rhizoctonia blight. However, significantly higher levels of disease were observed in plots treated with 48.8 kg N per ha per month than in those treated with 24.4 Kg N.