Foliar Application of Fungal Biocontrol Agents for the Control of White Mold of Dry Bean Caused by Sclerotinia sclerotiorum

Field experiments were conducted during 1992–1994 to evaluate the effectiveness of five indigenous fungi for control of white mold (Sclerotinia sclerotiorum) of dry bean (Phaseolus vulgaris). The five fungi consisted of one antagonist, Epicoccum purpurascens, and four mycoparasites, Coniothyrium minitans, Talaromyces flavus, Trichothecium roseum, and Trichoderma virens. Spore suspensions of each fungus were sprayed onto bean plants two or three times during the early bloom to midbloom period. Incidence of white mold of dry bean was significantly reduced by all biocontrol agents. C. minitans and E. purpurascens, the most effective agents, reduced the proportion of plants infected by an average of 56 and 43%, respectively (P < 0.001). C. minitans was the only biocontrol agent recovered consistently from sclerotia and diseased seed present in harvested samples. It was recovered at similar frequencies in samples from all treatments. Of the sclerotia of S. sclerotiorum collected from harvested seed, 59% were infected by C. minitans in 1993 and 20% were infected by C. minitans in 1994. In three additional trials in 1994, comparing C. minitans with the fungicide benomyl, the fungus was not effective in any of the experiments, whereas benomyl reduced disease incidence relative to the control in one trial. The study suggests that, among the five indigenous fungi, C. minitans is the most promising agent for control of white mold of dry bean under Canadian prairie conditions.