Bee Vectoring Technology Using Clonostachys rosea as a Biological Control for Botrytis Fruit Rot of Strawberry in Florida

Botrytis fruit rot (BFR), caused by Botrytis cinerea, is a major strawberry disease. The intensive use of fungicides for its management has resulted in resistance to several fungicide groups, requiring alternatives to BFR management. In this study, we evaluated the efficacy of bee vectoring technology (BVT) using Clonostachys rosea as a fungal biological control agent for BFR. BVT involves the use of bumble bees to carry C. rosea to strawberry flowers, where it can compete with B. cinerea. Three experiments were conducted on commercial farms in Florida during the 2016-17, 2017-18, and 2018-19 strawberry seasons. Treatments consisted of a nontreated control, fungicide standard program, BVT, and BVT + fungicide program. Fruits were harvested twice a week throughout the season to determine BFR incidence and yield, and postharvest activity was quantified during selected harvests. Temperature effect on mycelial growth was also determined for B. cinerea and C. rosea. The BVT + fungicide program reduced BFR incidence compared with the nontreated control in all seasons. However, BVT treatment by itself was not effective in improving yields or reducing disease incidence, likely due to highly favorable weather conditions for BFR in Florida. In addition, the low attractiveness of strawberry flowers to bumble bees and the fact that C. rosea is a better colonizer of strawberry leaves than flowers could also be limiting the effectiveness of BVT. Therefore, the BVT may be used in combination with fungicides to reduce BFR in strawberry production in Florida, but its cost-effectiveness still needs to be determined.