Mulching highbush blueberry with Trichoderma atroviride SC1-inoculated barks controls Armillaria root rot

One of the causes of Armillaria root rot diffusion on highbush blueberry in Trentino (Northern Italy) is represented by the use of infected coniferous barks as mulch. They are collected by growers in the forest and spread in field to control infesting grass and preserve low soil acidity. Trichoderma atroviride SC1 is a biocontrol agent against Armillaria root rot. Maintaining over time high inoculum of T. atroviride SC1 in soil and rhizosphere is difficult. Barks seem to be an appropriate substrate to prolong its survival. We demonstrated that no differences exist between highbush blueberries cultivated on Armillaria gallica infected soil or in healthy soil mulched by A. gallica infected coniferous barks. In vitro trials demonstrated that there are not differences in the control efficacy of T. atroviride SC1 against A. gallica when different type of barks (larch, pine, fir and their mixture) are used. T. atroviride SC1 can survive and grow on all types of bark for a long time after treatment. Trials under greenhouse conditions showed that the disease did not develop on strawberry plants mulched with mixed bark pre-inoculated with SC1 and inoculated with A. gallica. The disease incidence was reduced from 70% (untreated bark) to 25% (treated bark with T. atroviride SC1). The use of pre-treated barks with T. atroviride SC1 is a useful agronomic practice to prevent Armillaria root rots