Though over 60 plants serve as hosts of San Jose scale, apple, peach, pear, pyracantha, quince and cotoneaster are most susceptible. Scale insects feed on plants by inserting their stylets into leafy or woody tissues and continually withdrawing plant juices. San Jose Scale feeds on the fruit, foliage and bark of its host. Female scales are flat, circular and grayish with a darker nipple-like formation arising from their center.
Males are smaller and somewhat elongated Both males and females overwinter as immatures.
Scales become sexually mature and mate in the spring. Females give live birth to first generation crawlers in late June. Crawlers are yellow, flat and quite small. There are two or more generations per year. Oils can be used as dormant treatments in the spring.