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San Jose scale (SJS)

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Quadraspidiotus perniciosis

Overview

SJS infested bark has a grey, roughened appearance due to scale insects on limbs and trunk. Infested fruit develop a reddish-purple ring surrounding each spot where a scale settles.

Biology

  • Adult scales are round (females) or oval (males), about 1/16 inch in diameter, and greyish with a raised yellow nipple in the center. Immature SJS overwinter on twigs and branches under scale covering. Around Bloom, winged males emerge, seek out female scales, and mate.
  • Tiny, bright yellow nymphs or "crawlers" emerge in mid-late June. Each female produces several hundred living young which desperse over the tree in search of suitable feeding sites.
  • As crawlers mature they produce a whitish secretion which blackens with time and hardens into a waxy protective covering.
  • Second generation male flight and mating usually begins by mid-July, producing crawlers by mid-August.

Monitoring

  • Crawler emergence can be monitored using a band of black electricians' tape wrapped around an infested limb and coated with a thin layer of petroleum jelly. Tape should be inspected daily with a hand lens until active crawlers are found.
  • Decision to treat is usually based on finding infested fruit at previous year's harvest. Examine 50 fruits per tree on 2 trees per acre and treat if find more than 0.1% fruit with SJS injury.

Management

  • Thorough, yearly pruning helps manage SJS.
  • Established, heavy SJS populations are difficult to mange and may require both semidormant oil application and insecticide application targeting crawlers.
  • For best results, apply 60-70 sec oil (3 gal/100 gal ware for heavy infestation, 2 gal/100 for others) around Half Inch Green.
  • Apply insecticide when crawlers become visible. Some insect growth regulator insecticides have been very effective at controlling crawlers.