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Monitor San Jose Scale—Bloom to Postbloom

Male San Jose scale, Diaspidiotus perniciosus, caught in a pheromone trap.
Crawlers of San Jose scale, Diaspidiotus perniciosus.

The best time to assess the need for managing San Jose scale is during the dormant season. Dormant season is also the preferred timing for spray treatments. However, if a dormant spray was not applied and San Jose scale was a problem in your orchard in the previous season, or if the dormant treatment was not effective, a spray can be applied from late bloom to petal fall.

Use pheromone traps to time bloom treatments. These trap readings do not tell you if treatment is needed, but they help you to time treatment for best control in the spring. Use degree-days and pheromone traps to predict the crawler stage, and use sticky traps to confirm crawler activity.

Monitoring at this time will also help you keep track of the appearance and development of scale populations, as well as the level of parasitism by Aphytis and Encarsia.

When the traps begin to catch males consistently, start accumulating degree-days using a 51°F lower threshold and a 90°F upper threshold. If it is needed, apply a treatment for crawlers 600 to 700 DD after you catch the first males. Be aware that the traps may fail to catch any adults if the weather is cold, rainy, or windy.

To monitor for San Jose scale:

  • Put up pheromone traps between February 25 and March 1, positioning them well within the canopy to keep them out of the wind. Pheromone traps catch adult males, which are winged.
  • Place sticky tape in the trees in April to catch crawlers when they hatch.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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