How to Manage Pests
UC Pest Management Guidelines
San Jose Scale
Scientific Name: Quadraspidiotus perniciosus
(Reviewed 11/09, updated 11/09, pesticides updated 9/15, corrected 1/19)
In this Guideline:
Description of the Pest
The San Jose scale has no visible egg stage; scales emerge from under the edge of their mother's covering as nymphs. There are three stages during the first instar: the crawler, which is mobile and locates a feeding site; the white cap, which feeds and becomes covered with a waxy secretion; and the black cap, which is a darker, harder wax covering under which they may overwinter. The male scale will molt four times, and is elongate and black. The female molts twice, and is circular and gray. Males emerge as winged adults while the females remain wingless under the scale covering. There are three to four generations per season, taking about 7 to 8 weeks per generation.
Scales suck plant juices from twigs and limbs and inject a toxin, resulting in loss of tree vigor, growth, and productivity. They are found on wood with thin bark and fruit. A red halo is produced around a feeding site. Untreated infestations can kill a tree in 1 to 2 years.
In cherries San Jose scale is rarely a problem in most growing areas; it can be an occasional pest, however, in the southern San Joaquin Valley. A number of natural enemies help keep San Jose scale populations suppressed.
Calculate degree-days for San Jose scale in your location.
Learn to use degree-days to time insecticide applications.
A number of natural enemies help keep San Jose scale populations suppressed. Species of the parasitic wasps Encarsia (formerly Prospaltella) and Aphytis lay an egg under the scale cover. The parasite larva consumes the scale body, and the new adult parasite cuts a circular hole in the scale cover to emerge. Both larvae and adults of the twicestabbed lady beetle, Chilocorus orbus, and the small nitidulid beetle, Cybocephalus californicus, feed on scale crawlers and settled nymphs. Broad-spectrum pesticides applied during the summer may destroy natural enemy populations and result in increased scale infestations.
Organically Acceptable Methods
Oil sprays and biological control by native scale parasites are acceptable in organically managed orchards.
Monitoring and Treatment Decisions
Populations of San Jose scale can be controlled with oil in the dormant season. Additional pesticides are necessary only when populations are severe. Treat during delayed-dormant period if scale population or sooty mold was observed the previous year.
UC IPM Pest Management Guidelines:
Insects and Mites
J. A. Grant, UC Cooperative Extension, San Joaquin County
Acknowledgment for contributions to Insects and Mites:J. Colyn, Mid-Valley Ag. Services
M. Devencenzi, Devencenzi Ag. Pest Mgmt. and Research
P. McKenzie, Mid-Valley Ag. Services