Agriculture: Pistachio Pest Management Guidelines

Soft Scales

  • Black scale: Saissetia oleae
  • Brown soft scale: Coccus hesperidum
  • European fruit lecanium: Parthenolecanium corni
  • Frosted scale: Parthenolecanium pruinosum
  • Description of the Pest

    Brown soft scale is a mottled, yellow-brown when young, becoming darker at maturity. It has three to five generations per year and is often found on the nut. Adult scales are flattened and elongated, resembling a football sliced in half and about 1/8 inch (3.3 mm) in length.

    Black scale is similar in size to the brown scale, dark brown to black, later becoming more mottled black and brown. It has an H-shaped ridge on the dorsum. There is generally only one generation per year in the Central Valley. However, in some years two generations have been detected.

    Frosted scale is elongated, slightly humped, and has a waxy, white frostlike coating in spring. It is about 1/4 inch (6.4 mm) at maturity and has one generation per year. It is found in the warmer interior growing areas.

    European fruit lecanium is identical to the frosted scale but does not have the frosted coating. High temperatures early in summer will increase mortality of immature stages of European fruit lecanium.

    Immature stages of these scale species are very small (about 1/64 inch) and difficult to distinguish from each other; look for the adults nearby to determine which species is present. Soft scales molt twice before they reach maturity. The stage just before the adult is frequently referred to as the rubber stage. In this stage, the scales remain soft, somewhat translucent and are still susceptible to parasitism. Upon molting to adults, the shell hardens and becomes opaque.


    In spring, soft scales produce heavy amounts of honeydew, providing a substrate on which sooty mold grows. Sooty mold growth covers leaves and can affect photosynthesis. Moderate-to-high scale populations can also retard shoot growth and shell splitting. Scales are most common on vigorously growing trees.


    These scales are normally kept under control by native parasites. Because of the increase in the use of permethrin treatments for true bugs in pistachio, natural enemies of scales are more frequently killed, and soft scales are becoming more prevalent.

    Biological Control

    There are a number of effective parasites of these soft scales. Most are tiny parasitic wasps in the genus Metaphycus. Metaphycus luteolus destroys the scale in its early instars before it can reproduce or cause substantial injury. This parasite produces several generations during each scale generation. In addition, predators, including the predaceous lady beetle, Rhyzobius (Lindorus) lophanthae, and green lacewings, Chrysopa and Chrysoperla species, feed on these scales.

    There is a strong relationship between phytocoris bugs and soft scale. Where phytocoris bugs are plentiful, scale density is commonly low. During March and April, young adult soft scales (prior to forming their crustlike covering and laying eggs) and soft scale eggs are a primary food source for phytocoris bugs. In fall, phytocoris bugs feed on second-instar scales that are migrating from the leaves to the woody shoots.

    Organically Acceptable Methods

    Biological control and oil sprays in the dormant period are acceptable for use in an organically certified crop.

    Monitoring and Treatment Decisions

    In early to mid-January, examine one-year-old fruiting wood for live and parasitized scale paying special attention to previously infested areas. Look at 12-inch dormant shoots that are randomly selected from throughout the orchard.

    • A light-to-moderate population in early February would be an average of one to five live scale per inch of fruiting wood.
    • A heavy population would be an average of 10 or more live scale per inch.

    Other factors to consider when making treatment decisions are the age, vigor, and split nut percentages.

    Apply a dormant treatment in mid-February before the scales reach the rubber stage of development. For optimal control, treat frosted scale before its waxy coating develops, and treat European fruit lecanium before it reaches the rubber stage in late February.

    Depending upon weather conditions and scale pressure, re-treatment may not be necessary for 3 to 5 years.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (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, 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.
    (Omni Supreme Spray) 4–6 gal 12 0
    MODE OF ACTION: Contact including smothering and barrier effect.
    COMMENTS: No more than 6% v/v solution permitted as a concentrate. Oil application can advance bud break by 7 to 10 days. Treatments made in November through December have a minimal effect on bloom timing. Use a distillation range of 440 to 470.
    (Seize 35WP) 4–5 oz 12 21
    COMMENTS: Insect growth regulator.
    (Centaur WDG) 34.5–46 oz 12 60
    COMMENTS: A growth regulator. Most effective on crawlers.
    (Sevin XLR Plus) 4–5 qt 12 14
    . . . PLUS . . .
    NARROW RANGE OIL 0.7–2.5 gal 4 0
    MODE OF ACTION: Improves translaminar movement and insecticide persistence
    COMMENTS: Best results are obtained with the addition of the oil to the spray for high populations. Moderate populations have been successfully controlled with oil alone. When dormant oil is applied in January or February, trees bloom somewhat earlier in spring, and they become more susceptible to frost damage. If dormant oil applications are made earlier (November–December), the effect on bloom timing is minimized.
    ** Unless otherwise noted, apply with enough water to ensure adequate coverage.
    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 organically grown produce.
    * Permit required from county agricultural commissioner for purchase or use.
    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). For additional information, see their Web site at
    Text Updated: 10/14
    Treatment Table Updated: 10/14