Pest profile

San Jose Scale

Comstockaspis perniciosa · Hemiptera: Diaspididae[2]

Left uncontrolled, San Jose scale can kill limbs or even entire fruit trees in just a few years.[1]

San Jose scales, small round gray scale covers crowded on tree bark
San Jose scales, small round gray scale covers crowded on tree bark. (c) Zihao Wang, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Reddish blemishes on fruit at harvest point to damaging numbers on the tree.[1]
  • Purplish-red halos on young bark, and scarlet tissue under peeled bark, signal infestation.[1]

Where it lives

UK Extension covers it as an extremely important pest of apples, pears, peaches and plums.[1]

US map: public records from 1 state since 1990 (GBIF).

Biology and life cycle

Females give birth to tiny yellow crawlers that wander, settle and cover themselves with wax within a couple of days.[1]

There are two generations a year, and the second generation's crawlers emerge over a long period.[1]

Damage and signs

  • It injects a toxin as it feeds, discoloring bark and fruit.[1]

Health risk

It feeds on trees; UK Extension mentions no risk to people.[1]

Control

Traps and physical control

Black sticky tape wrapped around an infested limb shows when crawlers are active.[1]

Pesticides

Dormant oil sprays give effective control in apples; crawler sprays go on about a week after crawlers first appear.[1]

Common questions

What are the red spots on my apples?
Reddish blemishes at harvest can mean San Jose scale on the tree.[1]
Why does scale survive my sprays?
Once settled, crawlers secrete a waxy cover that protects them from pesticides.[1]

Sources

  1. University of Kentucky Entomology (ENTFACT), “San Jose Scale (ENTFACT-204).” entomology.mgcafe.uky.edu/ef204 (accessed 2026-10-06)
  2. iNaturalist, “Comstockaspis perniciosa taxon page (order and family).” www.inaturalist.org/taxa/1476210 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.