Recently San Jose scale (Quadraspidiotus perniciosus Comstock) has reemerged as a critical pest within Michigan apple orchards. San Jose scale is an excellent candidate for the development of pheromone-mediated mating disruption as an alternative strategy to insecticides, as it is a weak flyer, and the sex-pheromone is known and has been in use for decades as a monitoring tool. The response of male San Jose scale to increasing densities of ISOMATE® dispensers primed with San Jose scale sex pheromone was utilized to determine the mechanism of mating disruption for this pest in a two-year study. Dispensers were deployed in naturally infested apple orchard plots at six different rates from 0 to 926 per ha. The dispenser density experiment revealed that San Jose scale exhibits competitive mating disruption, as evidenced by the curvilinear decrease in the number of males caught in monitoring traps with increasing dispenser densities. In a separate efficacy experiment, two rates of the ISOMATE® dispenser were compared to one rate of CIDETRAK® dispensers and an untreated control. There was no statistical difference among dispenser rates or types, but all performed significantly better than the control. However, an assessment of their pheromone release rate over time revealed significant differences in their output levels throughout the season. This study also revealed that the first flight of male San Jose scale in southwestern Michigan occurred after petal fall in both 2020 and 2021. Further research is needed to determine how best to incorporate mating disruption into current apple pest management programs, but this work demonstrates the viability of pheromone-mediated mating disruption as a pest management tool for San Jose scale. It is anticipated that this research will enable manufacturers of mating disruption tools to start the process of registration for commercial use.
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