Pest description and damage San Jose scale was introduced to the U.S. on flowering peach in the 1870s. It is now a pest of all fruit trees and many ornamental and wild trees and shrubs throughout the U.S., particularly in hot, dry climates. San Jose scale can be differentiated from other scale insects by the scale (shell) that covers the adult females. The scale is hard, gray to black, and cone-shaped, with a tiny white knob in the center. There is a series of grooves or rings around the scale, and a purple halo to the bark around the scale.
Biology and life history San Jose scale overwinters in an immature state under a black shell. In spring, the tiny winged males emerge and mate with wingless females. Females give birth to live young about a month later (no eggs are seen). The young scale, or "crawlers," are very small, flattened, and yellow, and move around on bark and foliage before settling down to feed. A few days later, they secrete a waxy coating over their body for protection. From this point, female scale will not move. Crawlers are present during June and July and again in August to September; there are two generations per year.
Pest monitoring Inspect twigs during the dormant season when bark is more visible for these scale. Pay attention to weak plants. Observe the young bark for purplish-red halos, which indicate infestation. (In cherry orchards, leaves of infested trees do not drop in fall, making detection straightforward). Bark of infested trees becomes rough in texture (healthy bark even on older trees is smooth). The crawlers are best observed during June to July with a 10X magnifying glass. Crawlers can be monitored by wrapping a piece of black sticky tape around an infested branch with the sticky side out. Pheromone traps will trap males to provide early warning and there is a degree-day model for predicting when crawlers will emerge.
Ensure ample water and cultural care with proper pruning cuts and management.
Several parasitoids are known to attack this scale but in fruit growing regions they have not kept the San Jose scale population in check. In home orchards, where pesticides are precisely targeted, the parasitoid has been more effective.
See "Scale insect" in:
For more information
Hoyt, S. 1993. San Jose Scale. WSU Extension (http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=490)
Mayer, D. F. and J.D. Lunden. 1997. "V-71639 and Supracide for Control of San Jose Scale on Apples" in Proceedings of the 71st Annual Western Orchard Pest & Disease Management Conference (http://entomology.tfrec.wsu.edu/wopdmc/1997PDF/4-Chemical/Chemical%2097-...)
Smith, T. 2011. San Jose Scale. WSU Extension (http://county.wsu.edu/chelan-douglas/agriculture/treefruit/Pages/San_Jos...)