Populations of predatory and pest mites in first‐level and second‐level commercial apple orchard blocks in Massachusetts

Abstract

Abstract: Populations of predatory and phytophagous mites were sampled weekly throughout the growing season in first‐ and second‐level integrated pest management (IPM) blocks in 12 commercial apple orchards in Massachusetts in 1993. In first‐level blocks, insecticides were used throughout the growing season. In second‐level blocks, no insecticides were sprayed after early June. Among the 12 orchards, 92% contained Amblyseius fallacis, 8% contained Typhlodromus pyri and 50% contained Zetzellia mali as predaceous species, while 100% contained Panonychus ulmi and 58% contained Tetranychus urticae as pest species. When averaged over the entire season, populations of predaceous A. fallacis and Z. mali and populations of pest P. ulmi were numerically, but not statistically, greater in second‐level blocks than in first‐level blocks. The opposite was true for T. urticae. Initial time of appearance of each species was about the same in both types of blocks. Panonychus ulmi peaked in mid‐July, much earlier than A. fallacis, the most frequently observed predaceous mite. Populations of the latter peaked in September at relatively low densities, too late in the growing season for this species to provide, by itself, timely biological control of pest mites. Winter mortality from cold temperatures and spring/summer mortality from the use of fungicides are suspected to be the principal agents responsible for the slow build‐up of A. fallacis. Zetzellia mali was present in early spring and increased slowly until reaching peak levels in autumn. Absence of pre‐bloom oil and other acaricide sprays in a small portion of each second‐level block did not facilitate build‐up of predaceous mites, but did result in rapid build‐up of P. ulmi.