How to Manage Pests
UC Pest Management Guidelines
San Jose Scale
Scientific name: Diaspidiotus (=Quadraspidiotus) perniciosus
(Reviewed 3/09, updated 6/09)
In this Guideline:
DESCRIPTION OF THE PEST
There is no visible egg stage with this insect; the scales emerge as mobile nymphs. Crawlers are bright yellow and tiny (about the size of the sharp end of a pin), with well developed eyes, antennae, and legs. After locating a feeding site, the crawlers settle, begin feeding, and lose their antennae, legs, and eyes, becoming immobile. They soon begin to secrete a waxy substance that covers the body. Initially the waxy covering is white (white cap), but turns darker later in the first instar (black cap). Male scales have a more elongated covering than the females; males molt four times, whereas females have a rounder cover and molt twice. The male emerges as a winged adult and the female remains 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, and death of limbs. A red halo is produced around a feeding site on 1-year-old green wood. Untreated infestations can kill fruit spurs and scaffold wood within 1 to 3 years.
San Jose scale has many natural enemies that can frequently keep the pest under control if not disrupted by in-season applications of broad-spectrum insecticides. Many orchards that have not used broad-spectrum sprays for 2 or 3 years do not have San Jose scale problems. Low to moderate populations can be managed with oil sprays during the dormant season. The best time to spray is during the dormant season, and low-to-moderate populations can be managed with oil sprays at this time. The scale is monitored as part of the spur sample during the dormant season and with pheromone traps in the spring.
Natural enemies that feed on San Jose scale include two predaceous beetles: the twicestabbed lady beetle, Chilocorus orbus, and another small beetle Cybocephalus californicus. A number of small chalcid and aphelinid wasps, including Aphytis spp. and Encarsia (Prospaltella) sp., parasitize this scale. These predators and parasites are helpful in reducing scale populations, but insecticides used during the growing season for other pests disrupt this natural control, and scale populations can build as a result. Low winter mortality due to mild temperatures will also permit a buildup of scale populations.
Organically Acceptable Methods
Biological control and a properly applied oil spray during the delayed-dormant period are organically acceptable management practices for this pest.
Monitoring and Treatment Decisions
Monitor San Jose scale during the dormant season by collecting spurs and examining them for live scale as well as for tiny emergence holes, which indicate parasite activity. For details on dormant spur sampling and treatment thresholds, see the section Dormant Spur Sampling and the monitoring form .
For large-scale populations, a properly applied dormant spray with good coverage is the most effective, and will eliminate the spring flight and suppress the infestation throughout the growing season. Do not use oil sprays, however, on water-stressed trees. The following table gives a guideline for making treatment choices based on levels of infestation on dormant spur samples:
Oil alone can be effective in controlling low-to-moderate populations. If populations are high, include an insect growth regulator (pyriproxyfen-Esteem or buprofezin-Applaud) with the oil. Organophosphates are available but are associated with environmental problems and should be avoided. When the dormant organophosphate and oil spray is first omitted, San Jose scale populations tend to increase the first year, but by the second and third year parasite populations have increased to levels where they reduce San Jose scale populations and maintain them at low levels.
Calculate degree-days for San Jose scale in your location.
Learn to use degree-days to time insecticide applications.
If dormant or delayed-dormant controls were not applied, and monitoring indicates that scale densities may require treatment, use pheromone traps to detect male emergence in spring. Place traps 6 to 7 feet high in the north or east side of trees by February 25 in southern areas and by March 15 in the north. To time treatment, accumulate degree-days using a lower threshold of 51°F and an upper threshold of 90°F. The optimum time for spring spraying with an organophosphate is 600 to 700 degree-days (DD) after the beginning of the male flight or 200 DD after crawler emergence begins. Apply pyriproxyfen (Seize) and buprofezin (Centaur) at the beginning of crawler emergence, which is 400 DD from the beginning of the male flight. Sticky tape can be used to monitor crawlers when they hatch. Late-fall or postharvest treatments are not effective.
Parasite populations can also be monitored with San Jose scale pheromone traps in spring because the parasites are attracted to the traps. To distinguish the adult male San Jose scale from the parasite Aphytis spp., look for a dark band across the back of the male San Jose scale at the base of its wings.
UC IPM Pest Management Guidelines:
Insects and Mites
Acknowledgment for contributions to Insects and Mites: