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San Jose scale

Quadraspidiotus perniciosus (Comstock)
Hemiptera: Sternorrhyncha: Diaspididae

Adult males are minute, winged insects about 1 mm long and golden brown with a reddish tinge. Scales may be either disk-shaped (females) or oval (males), and are composed of concentric rings of gray-brown wax radiating from a tiny white knob (A). Nymphs (crawlers) are bright yellow and resemble spider mites (B).


Widespread and a major pest in most fruit-growing states and provinces in eastern North America.


Attacks apple, peach, pear, and plum. Scale infestations on the bark can be heavy and contribute to an overall decline in tree vigor, growth and productivity. Tree death is possible. Feeding on the fruit induces local red-to-purple discoloration around the feeding sites (C). Early season fruit infestations may result in small, deformed fruit.

Similar Species

Forbes scale (Quadraspidiotus forbesi) looks similar, but can be distinguished by a raised reddish area in the center of the scale. European fruit scale (Q. ostreaeformis), is also difficult to distinguish, although it tends to be lighter in color than San Jose scale.


Spray a delayed dormant oil when buds are showing green tissue but before pink bud. Insecticide applications may be made to control newly emerged crawlers in early summer. Use pheromone traps to monitor adult males. A degree-day developmental model can predict crawler emergence after petal fall or trap biofix.

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