| Summary: | Trials under controlled and field conditions were conducted to establish the effect of strategies of application of biological control agents (BCAs) in the reduction of <i>Stemphylium vesicarium</i> and <i>Pleospora allii</i> inoculum production on pear leaf debris. Six BCAs based on different strains of <i>Trichoderma</i> spp. (Tr1, Tr2) and <i>Bacillus subtilis</i> (Bs1, Bs2, Bs3 and Bs4) were evaluated. Two strategies were tested in controlled experiments: application before (preventative strategy) or after (curative strategy) pear leaf debris colonization by <i>S. vesicarium</i>, evaluating the growth inhibition and sporulation of <i>S. vesicarium</i> and the pseudothecia production of <i>P. allii</i>. When the BCAs were applied preventatively, the efficacy of treatments based on <i>B. subtilis</i> was higher than those based on <i>Trichoderma</i> spp. in controlling the pathogen colonization, but that of controlling the inoculum production of <i>S. vesicarium</i> and <i>P. allii</i> was similar. However, when the BCAs were applied curatively, <i>Trichoderma</i> based products were more effective. In field trials, <i>Trichoderma</i> spp. Tr1 and <i>B. subtlilis</i> Bs1 produced a consistent 45–50% decrease in the number of <i>S. vesicarium</i> conidia trapped compared to the non-treated control. We conclude that <i>Bacillus subtilis</i> Bs1 and <i>Trichoderma</i> spp. Tr1 and Tr2 can be expected to reduce fungal inoculum during the pear vegetative period by at least 45–50%. Additionally, <i>Trichoderma</i> spp. Tr1 and Tr2 have the potential to reduce the fungal overwintering inoculum by 80% to 90%.
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