Prelayby Applications of Experimental Fungicides for Suppressing Rhizoctonia Root Rot in Sugar Beet. E. G. Ruppel, Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Crops Research Laboratory, 1701 Center Avenue, Fort Collins, CO 80526. R. J. Hecker, Plant Geneticist, U.S. Department of Agriculture, Agricultural Research Service, Crops Research Laboratory, 1701 Center Avenue, Fort Collins, CO 80526. Plant Dis. 71:694-698. Accepted for publication 26 February 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0694.

In a 3-yr study, prelayby applications of experimental fungicides Bay NTN 19701, triadimefon, triadimenol, and Bay HWG 1608 suppressed Rhizoctonia root rot in sugar beet; suppression was more pronounced in a susceptible than in a resistant cultivar. Generally, Bay NTN 19701 and Bay HWG 1608 at 28 and 14 g a.i./305 m of row provided the most supression. In-furrow applications and those made at the cotyledon or four- to six-leaf stage provided more suppression than those made at layby, when the foliage nearly covered the furrows. A split application of these fungicides at half-rates per application was as effective as the application at the cotyledon stage, indicating that most of the effectiveness was due to the early treatment. Soil population densities of Rhizoctonia solani at harvest were correlated with disease severity and negatively associated with recoverable sucrose from sugar beet.