Field management of Sclerotinia stem rot of soybean using biological control agents

Biological control agents (BCAs) were evaluated for their efficacy on reducing the number of sclerotia of Sclerotinia sclerotiorum (Lib.) de Bary in the soil and on Sclerotinia stem rot in soybean production systems in Michigan. BCAs included Coniothyrium minitans CON/M/91-08 (Product name: Contans (R) WG), Streptomyces lydicus WYEC 108 (Actinovate (R) AG), Trichoderma harzianum T-22 (PlantShield (R) HC), and Bacillus subtilis QST 713 (Serenade (R) MAX). At two field locations, soil artificially infested with S. sclerotiorum sclerotia, was treated by incorporating the above BCAs in the topsoil before planting and boscalid was applied as a foliar fungicide at growth stage R1 as a positive control. C. minitans was the most effective BCA and reduced the disease severity index (DSI) by 68.5% and the number of sclerotia of S. sclerotiorum in the soil by 95.3%. S. lydicus and T. harzianum reduced DSI by 43.1% and 38.5% and sclerotia in soil by 90.6% and 70.8%, respectively. B. subtilis only had a marginal effect on S. sclerotiorum. Populations of Bacillus, Streptomyces, Trichoderma spp., and C. minitans collected from soil samples and at 3, 28, 71, and 169 days after BCA application indicated that the population of Streptomyces, Trichoderma spp., and C. minitans did not change significantly throughout the season, which may be the reason for their effectiveness. Published by Elsevier Inc.