Evaluating pheromone dispenser density and longevity for San Jose scale mating disruption in apple orchards

Abstract

San Jose scale (Comstockaspis perniciosus Comstock) (Hemiptera: Diaspididae) is a cryptic sap-sucking pest in temperate orchards. In recent years, San Jose scale has become more challenging to manage, in part due to the loss of registered insecticides and difficulty in timing insecticide applications with the appropriate life stage. For insects like San Jose scale whose sex pheromones are known, mating disruption presents a biorational alternative to insecticide use in orchards. In 2020 and 2021, we evaluated this approach for San Jose scale in on-farm trials in Michigan apple orchards. ISOMATE® twin-tube reservoir dispensers primed with San Jose scale mating pheromone were placed into small orchard plots with densities ranging from 62 to 926 per ha to determine optimum density for control. In both years, male capture using baited traps was significantly reduced in plots under mating disruption, suggesting competitive population suppression. Optimum density of dispensers was determined to be 247 per hectare. A separate comparison study of the ISOMATE® twin-tube and CIDETRAK® MESO pheromone dispensers showed comparable efficacy despite differing release rates between the two types of dispensers. However, higher rates did provide greater suppression during the lower population densities in the first generation. We suggest there is some flexibility with rate and dispenser types for efficacious control. We also provide updated information on the phenology of the male San Jose scale flight activity. These results provide evidence for the potential utility of pheromone mating disruption for managing San Jose scale in apple orchards and highlight focus for further optimization.