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Integrated Strategies to Control Bean Root Rot in Minnesota
April 15, 2002

By Consuelo Estevez de Jensen, James E. Kurle and James A. Percich, University of Minnesota

The effects of moldboard tillage and seed treatment on root rot of dry bean and soybean were evaluated during the 2001growing season.

Dry bean and soybean seed inoculated with a peat formulation of Bacillus subtilis MBI600 and Rhizobium leguminosarum RCR3622 were sown in a Verndale sandy loam soil that had either moldboard tillage or reduced tillage. The reduced tillage operation consisted of disking (5-6 in. depth), followed by harrowing (4-6 in. depth). Fertilization included 100 lb/A of N as urea applied half at sowing and half 45 days after sowing at Staples. No nitrogen was applied at Verndale.

At Staples and Verndale emergence of dry bean was unaffected by either tillage or seed treatment. Seed treatment reduced disease severity (scale 1-9, 1 = healthy, and 9 = dead plant) while tillage had no effect. At Staples disease severity for untreated vs. treated seed was 5.6 and 4.0, respectively in RT plots. In the moldboard tillage plots, disease severity was reduced from 5.0 (untreated) to 3.9 (treated seed). In highly infested soil at Staples moldboard tillage alone increased yield 142 lb/A when compared to conventional tillage (Table 1).

At Verndale, moldboard tillage alone increased dry bean yield by 540 lb/A (Table 1). At Verndale, dry beans had less root rot damage than at Staples. Dry bean seed inoculation with B. subtilis MBI600 plus Rhizobium RCR3622 in the moldboard tillage plots reduced disease severity from 4.6 to 3.9.

Tillage did not have a significant effect on soybean yield at Staples in 2001 (Table 2). When soybean seed was inoculated with B. subtilis MBI600 plus Bradyrhizobium RCR3407 disease severity was reduced. At Verndale DS in soybeans in both reduced tillage and moldboard tillage was also significantly reduced by seed treatment with B. subtilis MBI600 plus Bradyrhizobium RCR3407. Moldboard tillage reduced penetration resistance at 15 to 20 cm depth from 2000 Kpa in reduced tillage to 1,000 Kpa in MT plots, indicating that the impedance layer occurring at the Bt horizon was broken-up by tillage. At Verndale, seed inoculation with Bacillus subtilis and Bradyrhizobium japonicum increased soybean yields from 33 to 46 bu/A Table 2).

In two commercial grower fields with a history of bean root rot in Park Rapids and Verndale, Minn., two experiments were conducted to determine the effect of chisel tillage versus moldboard tillage and the use of Bacillus subtilis GBO3 (Kodiak) and Rhizobium inoculation on dry bean Montcalm. Each field was 15 acres arranged in a split plot design replicated six times. Main plots were tillage treatments 1) chisel tillage and 2) chisel tillage followed deep zone strip tillage. Subplots were the seed treatments 1) the standard seed treatment (SST) (Captan+Streptomycin +Lorsban) and 2) SST + Kodiak and inoculation with Rhizobium.

At both Verndale and Park Rapids tillage did not have a significant effect on bean yield (Table 3). However, seed treatment increased dry bean yields an average of 160 lb/A at Verndale and 280 lb/A at Park Rapids (Table 3). At Verndale and Park Rapids treated seed in MT plots increased yield 94 and 93 lb/A, respectively. While in the chisel tillage plots yield increased 231 and 466 lb/A, respectively.

In summary, the combined use of deep tillage and biocontrol seed treatments can alleviate the effects of root rot on dry bean and soybean.



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