Female scales are very prolific and can produce approximately 400 young over a 6-week period. The San Jose scale produces living young called "crawlers"; most other scales produce eggs. Crawlers move around for a short period in search of a suitable place to settle.
Two to three generations of the San Jose scale are born each year. The scale overwinters as immature "blackcaps"; adults mature during the bloom period. Males emerge and mate at apple petal fall. First-brood crawlers begin appearing in early June and continue for a month in southern areas of Pennsylvania. These crawlers develop into mature adults by late July. Second-brood adults appear from late July to early September; if a third brood occurs, it appears in late October to early November. The life cycle is completed in about 37 days. Crawlers usually can be found from early June until a hard frost in the fall.
Crawlers are lemon colored and very small (1/25 inch long). When they settle, they secrete a waxy substance that produces a grayish-yellow scale covering that becomes darker with age. The male scale is oblong, with a small black spot near one end, and is much smaller than the female. Color varies with age--very young females are round and nearly white but turn dark gray as they mature. A characteristic black spot appears in the center of the scale.
Scales on new vegetative growth and fruit produce deep purplish-red coloration in the tissue. When scales are removed from the fruit, a light-colored "bull's eye" is evident. Additional injury to the tree is caused by loss of plant sap, which depletes vigor and decreases yield. Prolonged attack causes the wood to crack and split; if the scale is not controlled, the tree might die.
Scales are especially difficult to control on large trees with rough bark. The secret to successful control is thorough pesticide coverage. If scales are present, the trees will benefit from an oil spray at the dormant or delayed-dormant period. Later in the season, usually from early to mid-June, the crawlers can be targeted if the oil sprays were less than effective. To accurately time these sprays, locate infested branches and wrap black electrician's tape around the branch at each end of the infestation. Coat the middle section of the tape with a very thin film of petroleum jelly. Check the tape often for the presence of crawlers trapped in the jelly. Apply an insecticide when the first crawler is observed.