San Jose Scale – Quadraspidiotus perniciosus

San Jose Scale – Quadraspidiotus perniciosus

Common Name: San Jose Scale

Latin Name:  Quadraspidiotus perniciosus


Crawlers are tiny, 1/25 inch long, and lemon-colored. When they settle, they release a waxy material that results in a grayish-yellow scale coating in the beginning and darkens over time. The male scale is significantly smaller than the female and is rectangular, with a tiny black patch towards one end. Age-related color changes occur; young females are rounded and almost white, but older females become dark grey. The scale has a recognizable black area in the middle.

Host plant:                 

Many hardwood trees and shrubs in the rose family (Rosaceae) may be infected, in addition to the usual hosts like apple, rose, pyracantha, cotoneaster, and crabapple.


The San Jose scale was discovered in North America for the first time in 1880 in San Jose, California. However, it is most likely native to China.

Damages caused by San Jose Scale:

Trees may suffer severe damage from massive-scale infestations, resulting in reduced strength, sparse foliage, broken or decaying limbs, and ultimately the loss of the tree. Young trees could die before bearing fruit. An infected fruit has a reddish purple ring around every place a scale settles.

Life history and habits:

San Jose scales overwinter as a nymph in the second larval stage. It begins to feed or grow in the spring when the sap starts to flow. Both nymphs and adults produce an armor-like layer of hard wax when eating. Larvae in their first stage are round and filthy white (“white caps”). In later phases, the color changes to gray-brown, and the central nipple becomes more apparent. The males’ coverings are much shorter and more elongated. Adults are tiny, flying insects that resemble gnats. Rapid development is possible; however certain organisms could have a brief latent phase. During Colorado’s growing season, three generations are most likely generated. There is a lot of overlap as the season goes on, and summer is when all phases may be found.