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How to Manage Pests

UC Pest Management Guidelines


Brown soft scale (above) and scale covering with parasite exit hole.

Pistachio

Soft Scales

Scientific names: Brown soft scale: Coccus hesperidium
Black scale: Saissetia oleae
Frosted scale: Parthenolecanium pruinosum
European fruit lecanium: Parthenolecanium corni

(Reviewed 2/07, updated 2/07)

In this Guideline:


DESCRIPTION OF THE PESTS

The brown soft scale is a mottled, yellow-brown color when young, becoming darker at maturity. It has three to five generations per year and is often found on the nut. It is flattened and elongated, resembling a football sliced in half. It is about 0.13 inch in length.

The black scale is 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.

The frosted scale is elongated, slightly humped, and has a waxy, white frostlike coating in spring. It is about 0.25 inch in length at maturity and has one generation per year. It is found in the warmer interior growing areas.

The 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.

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.

DAMAGE

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

MANAGEMENT

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 destroyed, 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, prey on these scales.

There is a strong relationship between Phytocoris plant bugs and populations of soft scales. Where Phytocoris plant bugs are plentiful, scale populations are commonly low. During March and April, immature adult soft scales and eggs are a primary food source for Phytocoris. In fall, Phytocoris feeds 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. 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 from mid-November through February before the scales reach the rubber stage of development. For optional 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/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees, impact of the timing on beneficials, and environmental impact Not all registered pesticides are listed. Always read label of product being used.
 
A. NARROW RANGE OIL#
  (Omni Supreme Spray) 6 gal 4 0
    4–6 gal    
  MODE OF ACTION: Contact including smothering and barrier effects.
  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 Nov.-Dec. have a minimal effect on bloom timing.
 
B. CARBARYL*
  (Sevin) 80S 5–6.25 lb 12 14
  (Sevin) XLR Plus 4–5 qt 12 14
  MODE OF ACTION: A carbamate (Group 1A)1 insecticide.
  ...PLUS...
  NARROW RANGE OIL 4–6 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  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 (Nov.–Dec.), the effect on bloom timing is minimized.
 
 
**  Unless otherwise noted, apply with enough water to ensure adequate coverage.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until harvest may occur. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest can take place.
* Permit required from county agricultural commissioner for purchase or use.
1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
Insects and Mites
W. J. Bentley, Kearney Agricultural Center, Parlier
R. H. Beede, UC Cooperative Extension, Kings County
K. M. Daane, Biological Control, UC Berkeley/Kearney Agricultural Center, Parlier
D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

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