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 effective ness of five indigenous fungi for control of white mold (Sclerotinia sclero tiorum) of dry bean (Phaseolus vulgaris), The five fungi consisted of one a ntagonist, Epicoccum purpurascens, and four mycoparasites, Coniothyrium min itans, Talaromyces flavus, Trichothecium roseum, and Trichoderma vi ens. Sp ore suspensions of each fungus were sprayed onto bean plants two or three t imes during the early bloom to midbloom period. Incidence of white mold of dry bean was significantly reduced by all biocontrol agents. C. minitans an d E. purpurascens, the most effective agents, reduced the proportion of pla nts infected by an average of 56 and 43%, respectively (P < 0.001). C. mini tans was the only biocontrol agent recovered consistently from sclerotia an d diseased seed present in harvested samples. It was recovered at similar f requencies in samples from all treatments. Of the sclerotia of S. sclerotio rum collected from harvested seed, 59% mere infected by C. minitans in 1993 and 20% were infected by C. minitans in 1994. In three additional trials i n 1994, comparing C. minitans with the fungicide benomyl, the fungus was no t effective in any of the experiments, whereas benomyl reduced disease inci dence relative to the control in one trial. The study suggests that, among the five indigenous fungi, C. minitans is the most promising agent for cont rol of white mold of dry bean under Canadian prairie conditions. (C) Minist er of Public Works and Government Services Canada 2000 and a 2000 Academic Press.