What are the best ways to manage Rhizoctonia solani of sugar beet?
M. F. R. KHAN (1). (1) North Dakota State University & University of Minnesota, Fargo, ND, U.S.A.
Rhizoctonia root rot caused by <i>Rhizoctonia solani</i> Kühn is the most important sugar beet disease for producers in Minnesota and North Dakota. There is no variety completely resistant to <i>R. solani</i>, and varieties with some levels of resistance are susceptible at seedling and early growth stages. Greenhouse and field research were conducted to evaluate fungicides as seed treatments, in-furrow application at planting, and foliar application. In both greenhouse and field studies, <i>R. solani</i> AG 2-2 IIIB grown on barley was used to artificially inoculate pots or the research site. Fungicides used included penthiopyrad as a seed treatment, and azoxystrobin at 167 g a.i ha<sup>-1</sup> applied in-furrow and or in a band application. In greenhouse studies, penthiopyrad consistently provided effective control as a seed treatment at rates of 7, 14 and 28 g a.i per 100,000 seeds. Azoxystrobin provided effective control when used in-furrow or in a band application. In field studies, penthiopyrad as a seed treatment followed by a band application of azoxystrobin provided similar effective control as azoxystrobin applied in-furrow followed by a band application. Penthiopyrad as a seed treatment was not effective at providing season-long control. The use of penthiopyrad, a succinate dehydrogenase inhibitor in a rotation program with azoxystrobin, a quinone outside inhibitor has the potential not only to provide effective control of <i>R. solani</i> but also to mitigate fungicide resistance.
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