How to Manage Pests

UC Pest Management Guidelines

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.

DAMAGE

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. A red halo is produced around a feeding site on 1-year-old wood. Untreated infestations can kill a tree in 1 to 2 years.

MANAGEMENT

A number of natural enemies help keep San Jose scale populations suppressed. Dormant sprays are recommended to manage scale population, followed by regular monitoring to see if populations are increasing and to assess the presence of biological control. Broad-spectrum pesticides applied during the dormant season or summer may destroy natural enemy populations, resulting in increased scale infestations; avoid these sprays where possible.

Biological Control
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   Degree-day calculator    Degree-day table
Monitor for scale regularly throughout the orchard. During the dormant season, check prunings from tree tops to see if scale infestations are developing. Look for dead leaves clinging to branches, a sign of heavy scale infestations. (Dead leaves may also cling to twigs killed by brown rot or other diseases.) You can assess the level of parasitism by taking 100 samples of second-year wood and estimating the proportion of scale insects that exhibit parasite exit holes. Because female parasites are attracted by the pheromone traps used to monitor for male scale (see below), you can use counts of parasites caught in these traps to assess the level of parasitism. During the season you can keep track of the appearance and development of scale populations by trapping crawlers with double-sided sticky tape.

Due to the damage potential of this pest, annual dormant sprays are recommended in most areas followed by regular monitoring to see if populations are increasing and to assess the presence of biological control. Dormant oil without organophosphates is effective against the white cap and black cap stages but will not control mature scales. Good spray coverage and sufficiently high application rates are essential for effective control; do not reduce dormant oil rates if scale is present. Control moderate to heavy populations of San Jose scale by applying an organophosphate insecticide with the oil spray.

If dormant sprays are not effective at controlling San Jose scale populations, or if they could not be applied, treat for the pest when the first generation of crawlers reaches a peak (usually early in May) as indicated by sticky tape traps or degree-day accumulations. Use pheromone traps for male scale, beginning by the end of February. Place the traps well within the canopy to keep them out of the wind. When the traps begin to catch males consistently, start accumulating degree-days using a 51°F (10.5°C) lower threshold and a 90°F (32°C) upper threshold. (For assistance in calculating degree-days (DD), see "Degree-days".) Apply a treatment for crawlers 600° to 700°DD after you catch the first males. The traps may fail to catch any adults if the weather is cold, rainy, or windy while they are active. Alternatively, you can monitor for crawlers using double-sided sticky tape. Place these sampling tapes adjacent to known scale infestations; the objective is not to monitor population changes, but to determine when crawlers begin to hatch. Begin to monitor with sticky tape early in April. Treat 200°DD after you detect the first crawlers.

If control of San Jose scale is a problem in the orchard, use a high-volume dilute application and apply it by ground.

PUBLICATION

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
Insects and Mites
R. A. Van Steenwyk, Insect Biology, UC Berkeley
K. M. Daane, Kearney Agricultural Center, Parlier
J. A. Grant, UC Cooperative Extension, San Joaquin County

Top of page