The interactions of Botrytis cinerea 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 28 ~ on grey mold of bean. All main effects and interactions were significant (P < 0.05) among the 72 treatments. In the control, lesions of grey mold developed under all environmental conditions but were largest at 24 ~ x 95 and 100% RH, and 28 ~ • 95% RH. Interactions of environment, BCAs and grey mold were complex. Alternaria alternata, Drechslera sp., Myrothecium verrucaria, Trichoderma viride, Gliocladium roseum and an unidentified pink yeast were all highly dependent on environment for biological control efficacy, and changes of 4 ~ or 5% RH were associated with variability in disease suppression that ranged from < 15 to 100%. Efficacy of Epicoccum purpurascens appeared independent of environment and this BCA suppressed disease by 100% in all of the environmental treatments. Suppression of grey mold by many of the BCAs was most effective under environmental conditions least conducive to disease. Therefore, evaluations of potential BCAs in environmental conditions that are marginal for disease can overestimate their efficacy in field environments. Assessments of biological control efficacy in various environments can be used to more accurately assess the potential of BCAs.

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