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Integrated management of Rhizoctonia in sugar beet: resistant varieties, seed treatments and postemergence fungicides

Ashok Chanda: Department of Plant Pathology, University of Minnesota

<div>Rhizoctonia damping-off and crown and root rot (RCRR) have been the most common root diseases on sugar beet in Minnesota and North Dakota. In 2017, a field trial was established to evaluate an integrated management strategy consisting of a resistant and moderately susceptible variety with seed treatments (penthiopyrad, sedaxane, and fluxapyroxad) in combination with postemergence (PE) azoxystrobin applied at the 4- or 8-leaf stage. Both varieties had similar stands up to 8 weeks after planting (WAP). Seed treatments and untreated control had similar stands at 2 WAP and by 3 WAP all the seed treatments had higher stands compared to the untreated control. At 5 WAP, sedaxane had highest stands, penthiopyrad and fluxapyroxad had intermediate, and untreated control had lowest stands. There were no significant differences between two varieties for stand data and harvest data. Root rot rating, yield, and other harvest parameters were not significantly different for the seed treatments and untreated control. Root rot severity and percent incidence were significantly lower with 4- or 8-leaf PE application compared to no PE. Yield, recoverable sucrose and percent sucrose were not significantly different between azoxystrobin and no azoxystrobin application. Results suggest an integrated approach utilizing a seed treatment to protect seedlings followed by a PE application for mid- to late-season disease pressure.</div>