Molly Arreguin, Anika Kinkhabwala, Philippe Rolshausen, Steven Lindow,
and Akif Eskalen*
*University of California, Davis, 1 Shields Ave, Davis, CA, 95616
(aeskalen@ucdavis.edu)

Pierce’s disease (PD) is a degenerative, deadly, and costly disease of grapevines caused by the Gram-negative bacterium Xylella fastidiosa subsp. fastidiosa (Xf). PD represents a major threat to the grape industry due to limited options for effective prevention and control in all grape regions of California. Biopesticides are an attractive solution for managing PD because they provide an alternative to strategies that use conventional agrochemicals for insect vector management and planting of PD-resistant grapevine. A field trial was performed in 2022 at UC Davis to test the effectiveness of different biopesticides for commercial application against PD. The trial included eight treatments plus two experimental controls. Treatments included XylPhi-PD, a commercially available bacteriophage-based biopesticide (A&P Inphatec) and OMRI-listed product that can directly target Xf, three beneficial biocontrols that showed promising results against PD under greenhouse conditions at UC Berkeley and UC Riverside, and different pairwise combinations of XylPhi-PD and each biocontrol agent. Each treatment was applied to ten 11-year-old Cabernet franc grapevines with four shoots per grapevine. All biopesticides were delivered to the vine using Xyleject. An 80 µL dose of each biopesticide was injected at the base of each shoot on both sides, following the XylPhi-PD label recommendation. Biopesticides were injected into grapevine one day pre-Xf inoculation and one-week post-Xf inoculation. Xf strain Stag’s Leap (~1 × 107 CFU/mL) was used for disease positive, and non-inoculated plants were used for disease negative controls to compare the efficacy of the treatments. The vines were inoculated with Xf using a drop puncture method of two 10 µL doses between the second and third nodes of the shoot. Our preliminary results indicate that vines treated with XylPhi-PD showed 50% fewer foliar symptoms than plants treated with the Xf pathogen alone. Moreover, XylPhi-PD and other biocontrol agents performed better when combined than either treatment applied alone.

Funding Support: California Department of Food and Agriculture, Pierce’s Disease and Glassy-Winged Sharpshooter Program, CDFA Agreement Number 22-0561-000-SA