Inoculum reduction of Stemphylium vesicarium, the causal agent of brown spot of pear, through application of Trichoderma-based products

In pear orchards, both pear-leaf litter and ground-cover litter support the production of conidia by Stemphylium vesicarium, the causal agent of brown spot of pear, and both are inoculum sources for epidemics throughout the growing season. The effect of Trichoderma-based products on S. vesicarium conidial production was investigated in the field and laboratory. Trichoderma was applied in spring to field plots in a grassy area naturally converted into a wildflower meadow and representative of ground cover in pear orchards. The plots had been previously inoculated with S. vesicarium by spraying the ground cover with the fungus and by adding fungus-colonized pear-leaf litter. In 2004 and 2005, conidia were trapped from May to August with spore traps placed above the ground. In both years, Trichoderma reduced the total number of conidia trapped relative to the control by about 50%. In laboratory experiments, dead pear and crabgrass (Digitaria sanguinalis) leaves were inoculated with Trichoderma, S. vesicarium, or with both fungi, and the production of conidia by the two fungi was quantified for 6 weeks. Trichoderma colonized both plants and produced abundant conidia. After 6 weeks, Trichoderma reduced production of conidia by S. vesicarium by > 99%. Trichoderma-based products seem very promising for reducing the S. vesicarium inoculum throughout the growing season.