Management of Dry Bean Root Rot in Minnesota April 01, 2001
Consuelo Estevez de Jensen, James E. Kurle, and James A. Percich, Department of Plant Pathology, University of Minnesota
Bean root rot has become more severe in Minnesota. Yield losses of as much as 50% have been observed in fields in highly infested areas. In Minnesota, root rot is caused primarily by the fungus Fusarium solani f. sp. phaseoli in association with F. oxysporum and Rhizoctonia solani. Increased root rot severity has been attributed to shortening of rotation intervals and use of susceptible cultivars.
We evaluated various combinations of a peat-based formulation containing Bacillus subtilis and Rhizobium, the standard seed treatment (SST) Captan plus Streptomycin and Lorsban and an untreated control. Two different B. subtilis strains (GBO3 and MBI600) alone or in combinations with R. tropici UMR1899 and R. etli RCR3622 were evaluated. Plant stands in the field were significantly increased with B. subtilis GBO3 plus R. etli RCR 3622 as well as with the B. sutilis GBO3 plus R. tropici UMR 1899 combination (Table 1). When either Rhizobium strain UMR1899 or RCR 3622 was used as an inoculant disease severity (DS) was reduced when compared to the untreated control (Table 1). Bean yields from seed treated with B. subtilis GBO3 plus R. etli RCR 3622 were significantly higher than yields of either the untreated control or SST (Table 1). The SST was not effective in controlling root rot and yields were similar to those of the untreated control. Captan appears to have limited effectiveness against root rot because it does not provide protection as the root elongates. Captan and Streptomycin may inhibit colonization by Rhizobia. The use of the co-formulated biocontrols of B. subtilis and Rhizobium strains may be a good strategy to maintain sustainable bean productivity and reduce the use of chemical seed treatments.
Table 1. Effect of seed treatments on bean root rot at Verndale, Minnesota