Effect of Lactofen, Azoxystrobin, and Genotypes on Charcoal Rot, Phomopsis Seed Decay, and Pod and Stem Blight in Soybean.

Yield-limiting diseases such as charcoal rot and Phomopsis seed decay have a significant impact on the economic potential for soybean because there are few methods for management of these diseases. The objectives of this study were to determine the development of charcoal rot, infection of seed by Phomopsis spp., and severity of pod and stem blight on Asgrow 4403, Delta Pine 5806, United States Department of Agriculture-introduced DT 97-4290 and plant introduction (PI) number PI 567562A, and Asgrow 4403 treated and not treated with lactofen or azoxystrobin. This is the first report of high levels of resistance in PI 567562A to charcoal rot, and resistance in this PI was greater than for DT 97-4290. Application of lactofen at growth stage R1 and azoxystrobin at either planting, R3, or R6 had no significant impact on severity of charcoal rot, percentage of harvested seed infected by Phomopsis spp., or severity of pod and stem blight on genotype Asgrow 4403. Of four genotypes evaluated, none were resistant to infection by Phomopsis spp. The genotypes Asgrow 4403, DP 5806, and DT 97-4290 were susceptible to pod and stem blight and PI 567562A was resistant.