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Integrating Biological Control of Armored Scale Pests of Christmas Trees

Armored scales are now more manageable in Christmas tree plantings, because of this and prior research, some of which was funded by the RCTB. Three insecticides were found to be effective as a two-spray program (acetamiprid, afidopyropen, and pyriproxyfen) for targeting crawler activity during the summer. All of these insecticides have reduced pollinator toxicity, relative to the dinotefuran standard, and so are more appropriate for use in summer foliar sprays. These active ingredients were found to be mediocre at suppressing scale populations when used in a single spray application in mid-August with or without horticultural oil, and horticultural oil was not found to be effective (at a 70 gallon per acre spray volume containing 2% oil). Acetamiprid is more effective against scales but is a less selective insecticide than pyriproxyfen, which is known to be compatible with parasitoid wasps, or afidopyropen, which should be compatible with predatory beetles. An effective strategy to make the best use of acetamiprid was trialed by growers in 2022 and 2023 by applying a full foliar spray about the time of bud break, based upon the superior timing effectiveness identified through previous work. The result was extraordinarily effective suppression of scale populations, while still permitting survival and effective parasitization of remnant patches of scales (possibly surviving due to inadequate spray coverage) later in the season. Manipulation of parasitoid populations via mass rearing and making field releases was not found to be feasible or cost effective. However, parasitoid wasps readily colonize scale infestations on commercial farms and can be used in an integrated pest management program, as long as use of broad-spectrum insecticides like bifenthrin are curtailed. Therefore, the most effective strategy for managing armored scales, as observed from large-scale grower experience, combines the most active insecticide, acetamiprid, applied at the most effective timing, which is close to bud break. For most fields, this one-spray program provides exceptional control of armored scales. Furthermore, acetamiprid is much less toxic to pollinators than the alternative scale insecticide dinotefuran, and at this spray timing acetamiprid replaces the use of the bee- toxic imidacloprid for managing balsam twig aphids. To avoid insecticide resistance to acetamiprid, growers should carefully monitor fields where this strategy is used and should plan to follow-up with two thorough applications of pyriproxyfen during periods of crawler activity to spot-treat areas where scale populations persist.

  • Project ID21-01-CAES
  • CategoriesInsect Management
  • Growing Region(s)Northeast
  • Tree SpeciesFir
  • Investigator(s)Cowles
  • Institution(s)The Connecticut Agricultural Experiment Station
  • Research Year2021
  • Publication Year2021
  • ReportDownload 📁