Agriculture: Nectarine Pest Management Guidelines

San Jose Scale

  • Diaspidiotus (=Quadraspidiotus) perniciosus
  • Description of the Pest

    Female San Jose scale lay eggs that hatch immediately and the young emerge from under the edge of the adult scale covering. These tiny, yellow crawlers wander in a random fashion until they find a suitable place to settle. Immediately upon settling, the crawlers insert their mouthparts into the host plant and begin feeding and secreting a white, waxy material (white cap stage); eventually the waxy covering turns black (black cap stage).

    San Jose scales overwinter predominantly (80%) in the black cap stage, although in mild years some adult females may also survive. In late January, nymphs resume their growth, molting two or three times before becoming adults in March. Immature male and female scales are indistinguishable until after the first molt when the body of the male begins to elongate. Males molt a total of four times after which yellowish, winged adult males emerge to mate with females. The adult female San Jose scale remains under its shell, which is gray and circular; the body under the shell covering is yellow. After mating, females produce eggs, which remain within the female body and hatch there. The crawlers emerge from the female. Crawlers from the overwintering females begin hatching in April, with their peak emergence usually in early May. There are usually four to five generations per year. Crawlers may be present throughout the summer and fall.


    San Jose scales cause injury by feeding on twigs, branches, and fruit; they may also inject salivary toxins while feeding.

    Heavy populations on the bark can cause gumming and kill twigs, branches, and entire trees if left uncontrolled. A characteristic, red halolike discoloration often forms around the insect on small twigs or infested fruit. Fruit with haloes will be culled because of its unsightly appearance.


    San Jose scale has many natural enemies that can frequently keep the pest under control if not disrupted by application 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. The best time to spray is during the dormant season when low-to-moderate populations can be managed with oil sprays, which don't destroy the scale parasites. The scale is monitored as part of the shoot sample during the dormant season and with pheromone traps in spring.

    Biological Control

    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 broad-spectrum 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 in the Dormant Season

    • Monitor San Jose scale during the dormant season by collecting shoots and examining them for live scale and for tiny emergence holes that indicate parasite activity.
    • For details on dormant shoot sampling and treatment thresholds see DORMANT SHOOT SAMPLING and record results on a monitoring form (PDF).

    Because of the damage potential of this pest, annual oil sprays during the dormant or delayed dormant period are recommended in most areas. For large-scale populations, a properly applied dormant spray with good coverage is the most effective timing and will eliminate the spring flight and suppress the infestation throughout the growing season. The following table gives a guideline for making treatment choices based on levels of infestation on dormant shoot samples:

    Treatment threshold Treatment
    Harvested before June 15 Harvested after June 15  
    below 20% below 5% no treatment
    20-60% 5-10% oil at 6 gal/acre
    over 60% over 10% oil at 2-6 gal/acre
    plus insect growth regulator1
    1 Using oil at the 4-6 gal rate will help prevent development of resistance to the IGR. If oil is used at the 2 gal rate, do not use the IGR in consecutive years to prevent resistance development.

    Oil alone can be effective in controlling low-to-moderate populations (apply before the third week of January). If populations are high, include an insect growth regulator (pyriproxyfen-Esteem, Seize; buprofezin-Centaur) 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 may 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. If you notice parasitized scale in your dormant sample, be sure to only use an insect growth regulator during the growing season.

    Monitoring and Treatment Decisions in the Growing Season

    • Monitoring with pheromone traps from late bloom until petal fall will help you keep track of the appearance and development of scale populations as well as the level of parasitism (Aphytis and Encarsia) but does not tell you if treatment is needed.
    • Need for treatment is better assessed during the dormant season and delayed dormant sprays are the preferred timing for treatment.
    • If inadequate control is achieved with the dormant spray or the dormant spray is not applied, treatment is also effective when applied soon after the emergence of crawlers in May.
    • Late season sprays to control San Jose scale are not recommended.

    Monitoring with traps

    Monitor scales by putting up pheromone traps around February 25 (see PHEROMONE TRAPS) and placing sticky tape in the trees in April. Place pheromone traps well within the canopy to keep them out of the wind. San Jose scale pheromone traps also attract both male San Jose scale and scale parasites (Aphytis melinus and Encarsia perniciosi). Adult male scale can be distinguished from parasites by the presence of a dark line across their thorax where the wings attach. (View photos of San Jose scale and parasites)

    Degree-day accumulation

    When the traps begin to catch males consistently, start accumulating degree-days using a 51°F lower threshold and a 90°F upper threshold. If it is needed, apply a treatment for crawlers 600 to 700 DD after you catch the first males. Confirm the presence of crawlers by checking sticky tape traps. Be aware that the traps may fail to catch any adults if weather is cold, rainy, or windy. Total generation time for San Jose scale is 1050 DD.

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

    "May" sprays

    If "May" sprays are required, use a high-volume (dilute) application at 400 gallons or more per acre for best coverage; do not use a low-volume application.

    Fruit samples

    Examine fruit on trees every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program, see FRUIT EVALUATION AT HARVEST. Record results (PDF) for harvest sample.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (conc.) (dilute) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies and honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
    If San Jose scale is a problem in the orchard, use a high-volume (dilute) application at 400 gallons or more per acre for best coverage.
      (440 or higher) 1.5 gal 12 0
      MODE OF ACTION: Contact including smothering and barrier effects.
      COMMENTS: Apply in a dilute application, using a total of 6–8 gallons of oil/acre. Choose a narrow range oil with a 50% distillation point of 440 or higher for dormant season use. Always check with your certifier as to which oils are organically acceptable. Provides about 80% control; use for light to moderate infestations. Apply before late January when most of the scales are in black cap stage. An option for orchards where bloom sprays of Bacillus thuringiensis or other selective larvicideare planned for control of caterpillars and no broad-spectrum pesticides are used in the orchard, thus allowing beneficials to keep scale at low levels.
      (440 or higher) 3–6 gal 0.5–1.5 gal 4 0
      MODE OFACTION: Contact including smothering and barrier effects.
      COMMENTS: Choose a narrow range oil with a 50% distillation point of 440 or higher for dormant season use. Using oil at the higher rates (4-6 gal/acre) will help prevent the development of resistance to the IGRs. If oil is used at the 2 gal/acre rate, do not use IGRs in consecutive years to prevent resistance development.
      . . . PLUS . . .
      (Seize 35WP) 4–5 oz/acre 12 14
      COMMENTS: An insect growth regulator that targets egg hatch. Good coverage is essential for good control. Do not apply more than three applications per growing season. Use allowed under a supplemental label.
      . . . or . . .
      (Centaur) 34.5 oz/acre 12 14
      COMMENTS: An insect growth regulator that is effective against nymphal stages. Good coverage is essential. Do not apply more than 69 oz/acre per year.
      (Seize 35WP) 4–5 oz/acre 12 14
      COMMENTS: An insect growth regulator; apply when scale crawlers first emerge. Do not apply more than three applications per growing season closer than 14 days apart. Good coverage is essential for good control.
      (Centaur) 34.5 oz/acre 12 14
      COMMENTS: An insect growth regulator that is effective against nymphal stages. Good coverage is essential. Do not apply more than 69 oz/acre per year.
      (Diazinon 50W) 3–4 lb 1 lb 5 days 21
      COMMENTS: Not allowable for use by many canneries. Avoid drift and tailwater runoff into surface waters. Where nectarines are grown adjacent to waterways, do not use this material. Apply with oil to reduce the risk of resistance development.
      (Sevin XLR Plus) 3–4 qt/acre 12 1
      COMMENTS: Will cause mite outbreaks. Not recommended for routine use, especially early in the season. Apply with oil. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
    ** For dilute applications, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre, or lower if label allows.
    * Permit required from county agricultural commissioner for purchase or use.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    # Acceptable for use on organically grown produce.
    Not recommended or not on label.
    1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).

    Important Links

    Text Updated: 06/10
    Treatment Table Updated: 09/15