San Jose Scale

Mobile crawlers emerge from beneath the adult female scale cover. 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 numbers of scale can be managed with oil sprays during the dormant season. The best time to spray is during the dormant season, and low to moderate numbers can be managed with oil sprays alone 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. Small chalcid and aphelinid wasps parasitize this scale, including some species of Aphytis and Encarsia (=Prospaltella). These natural enemies are helpful in reducing scale numbers, but insecticides used during the growing season for other pests disrupt this natural control, and scale numbers can increase as a result. Low winter mortality due to mild temperatures will also permit a buildup of scale numbers.

Biological control and a properly applied oil spray during the delayed-dormant period are organically acceptable management practices for this pest.

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 (PDF).

For high numbers of scale, a properly applied dormant spray with good coverage is the most effective spray timing 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 numbers. If numbers are high, include an insect growth regulator (pyriproxyfen, Seize or buprofezin, Applaud) with the oil. Organophosphates are effective and available but are associated with water runoff concerns and should generally be avoided. When the traditional dormant organophosphate and oil spray is skipped, San Jose scale numbers tend to increase the first year, but by the second and third year parasite numbers have increased to levels where they reduce San Jose scale numbers and maintain them at low levels.

• Use pheromone traps to detect male emergence in spring if monitoring indicates that scale densities may require treatment and dormant or delayed-dormant controls were not applied.
• 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 this 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 degree-days after crawler emergence begins.
• Apply pyriproxyfen (Seize) and buprofezin (Centaur) at the beginning of crawler emergence, which is 400 degree-days from the beginning of the male flight.
• Use sticky tape to monitor crawlers when they hatch.
• Late-fall or postharvest treatments are not effective.

Degree-days

Calculate degree-days for San Jose scale in almond for your location using the San Jose scale pest model. To learn more about using degree-days to time insecticide applications, watch the degree-days video.

Parasite numbers 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.

• Degree-day calculator
• Degree-day table
• Dormant spur sampling (PDF)
• Pheromone traps
•  Using degree-days to time insecticide applications