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Influence of Air Temperature and Relative Humidity on Biological Control of White Mold of Bean (Sclerotinia sclerotiorum). D. J. Hannusch, Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada; G. J. Boland, Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Phytopathology 86:156-162. Accepted for publication 22 October 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-156.

The interactions of Sclerotinia sclerotiorum and seven biological control agents (BCAs) were examined in controlled environments to determine the influence of selected relative humidities (RH) (90, 95, and 100%) and air temperatures (20, 24, and 28ēC) on biological control of white mold of bean. All main effects and interactions were significant (P = 0.0001) among the 72 treatments. In the control treatment, lesions of white mold developed in all environmental treatments but were largest at 20ēC × 100% RH, 24ēC × 95 and 100% RH, and 28ēC × 95% RH. Interactions of environment, BCAs, and white mold were highly complex. Alternaria alternata, Drechslera sp., Myrothecium verrucaria, Trichoderma viride, Gliocladium roseum, and an unidentified pink yeast were all highly dependent on environment for efficacy. Changes of 4ēC or 5% RH were associated with variability in disease suppression that ranged from =25 to 100%. Epicoccum nigrum was comparatively independent of environment and suppressed disease by 100% in all environments. Suppression of disease by many of the BCAs was most effective under environmental conditions that were least conducive for disease. Assessments of biological control efficacy in various environments can be used to more accurately assess the potential of individual BCAs.

Additional keywords: environmental interactions, Phaseolus vulgaris.