Insecticide and repellent tests on Washington leafhopper vectors of cherry X-disease

A recent outbreak of X-disease, caused by the phytoplasma "Candidatus Phytoplasma pruni," has severely harmed stone fruit production in the Pacific Northwest region of the United States. X-disease is spread by leafhopper vectors, primarily Colladonus montanus reductus in Washington and Euscelidius variegatus in Oregon. Growers rely on frequent insecticide applications and removal of infected trees, but these management recommendations originate from California when the last outbreak occurred in the 1980s. To update insecticide efficacy information for X-disease vectors, we evaluated 23 commercially available insecticidal products via direct spray, spray residues, systemic uptake by plants, or repellency assays. In direct spray bioassays, insecticides containing pyrethrins, pyrethroids, neonicotinoids, or organophosphates caused 100% mortality of C. m. reductus after 24 h. More selective chemistries including cyantraniliprole, flonicamid, and botanical essences also caused high mortality (>70%) of C. m. reductus (Van Duzee). For residues, neonicotinoids and pyrethroids caused the greatest mortality (≥70%) of C. m. reductus. Systemic uptake of neonicotinoids caused significantly higher mortality (51.4% to 100%) than controls (1.4% to 32.4%) of C. m. reductus. Direct sprays and 5 d residues of neonicotinoids caused high mortality (>70%) of E. variegatus. Cherry leaves treated with either kaolin clay or diatomaceous earth had 80% to 90% fewer C. m. reductus residing on them than the controls. Overall, pyrethroids and neonicotinoids were the most effective, but more selective chemistries and repellent clays showed potential and need to be validated in field conditions. Future work should integrate insecticides, repellents, and cultural tactics with phenology-based treatment timings to improve management sustainability.