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Mites

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Panonychus ulmi & Tetranychus urticae

Overview

European red mites (ERM) and Twospotted spider mites (TSM) are the two most common mite pests in New England orchards. Spider mites suck leaf fluids and chlorophyll, resulting in "bronzed" foliage. Slightly damaged leaves cause little or no adverse effect to crop. Extensive leaf bronzing results in decreased photosymthesis, often causing reduced fruit size, premature drop and reduction in fruit set the following year.

Biology

  • ERM overwinter as eggs on smaller branches, twigs, and roughened bark of apple trees. Egg hatch begins at Tight Cluster, is about half complete by Pink, and is complete by Petal Fall.
  • TSM overwinter as adult females primarily in orchard ground cover, where they feed on weeds and grasses. In mid-late summer, TSM migrate into fruit trees and feed on leaf undersides. There may be 10 generations per season.

Monitoring

  • Mite injury during the weeks following Petal Fall can damage fruit crop. Monitor mite populations by examining underside of fruit cluster leaves through May and June. Action threshold is 1-2 motile (not eggs) mites per leaf or 30% of leaves with one or more mites.
  • Starting in July, examine middle aged leaves for motile mites. Threshold for July is 5 mites per leaf. August 1-15 threshold is 7.5 mites per leaf.
  • Mites tend to build up during periods of hot, dry weather. Mite populations tend to build up in "hot spots" rather than uniformly throughout a block. Hot spots tend to form on trees adjacent to dusty, dirt roads and in certain cultivars such as Red Delicious and Empire.

Management

  • Oil is recommended at the 2-3 gal rate during the dormant period. Use 2 gal rate until Tight Cluster and reduce to 1 gal rate from Tight Cluster to Pink. Good coverage is essential (300 gal/A recommended).
  • Many beneficial insect and mite species prey on pest mites and provide some level of biological control. Minimizing the use of pesticides harmful to mite predators is critical for conserving natural enemies and enhancing biological control of mites. A predator/prey ratio of 1:10 may provide adequate biological control.
  • Several miticides are limited to 1 application per season to delay pesticide resistance developing.