Effects of dormant insecticide treatments on the San Jose scale (Homoptera: Diaspididae) and its parasitoids Encarsia perniciosi and Aphytis spp . ( Hymenoptera: Aphelinidae )

Populations of the San Jose scale (SJS), Quadraspidiotus perniciosus (Comstock), and its parasitoids, Encarsia perniciosi (Tower) and Aphytis spp. were monitored with double-sided sticky tape and pheromone traps in an almond orchard. A total of 1.21 ha plots within the orchard were treated during winter dormancy with several insecticides, including horticultural mineral oil alone, oil combined with the organophosphate diazinon at different dilution rates, and oil combined with the pyrethroid esfenvalerate in a completely randomized block design. Higher volume diazinon applications (3750 and 1870 l ha -1 ) proved effective against SJS crawlers, as did esfenvalerate. The higher volume applications had greater deposition on Kromecoat ® cards placed in the top of the tree canopy, where SJS is most abundant. The lower-volume (935 l ha -1 ) application of diazinon provided control of first-generation crawlers similar to the other diazinon applications, but it was generally less effective in controlling subsequent generations. All insecticide treatments were associated with a reduction of parasitoid numbers, especially the esfenvalerate application.