Formulation Specialist, R&D Department, Prophyta GmbH-Biologischer Pflanzenschutz GmbH, Malchow/Germany
Professor, Department of Plant Sciences and Plant Pathology, Agricultural Biosciences Building, P.O. Box 173150, Montana State University, Bozeman 59717-3150
Former Graduate Student, Department of Plant Sciences, ABS Bldg., P.O. Box 173150, Montana State University, Bozeman 59717-3150
Joyce L. A.
Montana Eastern Agricultural Research Center, Sidney
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Accepted for publication 14 March 2001.
Rhizoctonia crown and root rot, caused by the fungus Rhizoctonia solani AG 2-2, is one of the most damaging sugar beet diseases worldwide and causes significant economic losses in more than 25% of the sugar beet production area in the United States. We report on field trials in the years 1996 to 1999 testing both experimental fungicides and antagonistic Bacillus sp. for their potential to reduce disease severity and increase sugar yield in trials inoculated with R. solani AG 2-2. Fungicides were applied as in-furrow sprays at planting or as band sprays directed at the crown at the four-leaf stage, or four- plus eight-leaf stage, while bacteria were applied at the four-leaf stage only. The fungicides azoxystrobin and tebuconazole reduced crown and root rot disease by 50 to 90% over 3 years when used at rates of 76 to 304 g a.i./ha and 250 g a.i./ha, respectively. The disease index at harvest was reduced and the root and sugar yield increased with azoxystrobin compared with tebuconazole. The combination of azoxystrobin applied at 76 g a.i./ha and the Bacillus isolate MSU-127 resulted in best disease reduction and greatest root and sucrose yield increase.
© 2001 The American Phytopathological Society