How to Manage Pests

UC Pest Management Guidelines

Pistachio

Small Plant Bugs

Scientific names:
Western tarnished plant bug (lygus bug): Lygus hesperus
California buckeye bug: Neurocolpus longirostris
Calocoris bug: Calocoris norvegicus
Phytocoris bug: Phytocoris spp., including P. relativus and P. californicus
Psallus vaccinicola

(Reviewed 10/14, updated 10/14)

In this Guideline:


DESCRIPTION OF THE PESTS

A variety of small plant bugs in the family Miridae attack pistachio. The particular species varies depending upon location and natural vegetation. All of these bugs have a small, triangular-shaped marking on the back.

California buckeye bug adults are straw colored, slightly hunched, and about 1/3 inch (8.5 mm) in length. They often overwinter as eggs at the base of buds or leaf-petiole scars on 1-year-old pistachio wood. The nymphs are greenish with brown markings on the back. Both immatures and adults are easily identified by the relatively long, hairy first antennal segment and brown and white bands on legs and antennae. California buckeye bugs have been found only in orchards near their native plant hosts: California buckeye and Rhamnus species. However, once established in a pistachio orchard, buckeye bug will overwinter there.

Lygus bug adults are about 1/4 inch (6.4 mm) in length, vary from brownish to green, and it has a yellowish, triangular-shaped area on the back between the wings. They are most commonly found near alfalfa and beans, or plants such as clovers, Russian thistle, tarweed, London rocket, and lupine. Lygus bugs usually migrate into a pistachio orchard from nearby weeds. When rainfall and spring temperatures are ideal for the growth of broadleaf weeds, lygus bug numbers can be very high. When they move into the orchard, they tend to stay in the cover crop and move into the trees when the cover crop becomes unsuitable.

Calocoris bug adults are about 1/4 inch (6.4 mm) in length with a green body. The wings have a reddish brown tint and are black where they overlap. There are also two black dots on the thorax. Calocoris bug is usually found on mustard, wild radish, and vetch hosts and is most common in the northern San Joaquin and Sacramento valleys. Calocoris bug does not overwinter in pistachio trees but migrates into the orchards as native weed hosts dry or are cultivated in spring.

Phytocoris bugs overwinter in the egg stage on one-year-old fruit wood on pistachios as well as on other deciduous trees. Adults are about 1/4 inch (6.4 mm) long and are predominantly gray with flecks of black and white; they have long antennae and legs and can move rapidly when disturbed. The nymphs are also gray with white bands on the legs and antennae. Moderate numbers of phytocoris bugs are not considered damaging and seldom require treatment. They are predators of other insects, especially immature soft scale in March and April and second-instar scales that are migrating from leaves to woody shoots in fall; they also feed on navel orangeworm eggs in spring.

The least common of these small plant bugs is Psallus vaccinicola (there is no common name). The adults are about 1/8 inch (3.3 mm) long and are brownish red in color. They have been found predominantly near oaks in the Sacramento Valley.

DAMAGE

These bugs only cause damage for a short period of time, from bloom through shell hardening (early April–late May). However, during cool springs shell hardening is delayed and injury from plant bugs may be extended until June.

Small plant bugs insert their mouthparts into the nut, causing damage known as epicarp lesions, which on the inside of the nut appear as white netting. This damage is done before shell hardening and, except for damage caused by California buckeye bug, is more random in occurrence than damage caused by leaffooted plant bugs and stink bugs. Damage to small nuts results in blackening and nut drop. As the nuts enlarge, the hull tissue turns brown and necrotic, and the outside will often become sunken. On the inside of the nut there will be a small black spot or irregular-shaped pit in the area where the bugs fed on soft shell tissues.

MANAGEMENT

Careful attention to vegetation in and around orchards is the key to effective management of small plant bugs. The general pattern of bug appearance and distribution in an orchard is that phytocoris bugs and California buckeye bug overwinters in the trees. Calocoris and lygus bugs overwinter on preferred weed hosts in the ground cover. As vegetation in the pistachio orchard or surrounding areas dries, these bugs can move into the orchard canopy where they damage the developing crop.

Options to consider are

  • Elimination of all herbaceous vegetation
  • Maintenance of monitoring strips
  • Use of trap crops with insecticides
  • Use of cover crops that are not attractive to pest insects

Success or failure of each option will likely depend on the specific site and the species of bugs in the orchard.

Organically Acceptable Methods

Careful cover crop management is an organically acceptable management strategy. Mowing ground cover before bloom reduces small plant bug numbers.

Monitoring and Treatment Decisions

Monitor from early April until late May when shells harden and plant bugs no longer cause damage.

  1. Sample the trees with a beating tray.
    1. Hold the tray under nut clusters while striking the limb sharply three times with a lightweight club.
    2. Examine bugs that drop onto the tray.
    3. The best time to take beat samples is in the morning when bugs are less active and easier to examine.
  2. Sample the cover crop and surrounding vegetation with a sweep net for lygus bug and calocoris bug.
  3. Phytocoris bugs can also be monitored with pheromone traps, but research has not been done to correlate trap catches with economic injury.
  4. Look for small damaged or blackened nuts. Cut them open to confirm bug damage (black lesions inside the hull).

There are currently no treatment guidelines based on the number of small plant bugs found.

  • If populations are found uniformly throughout the orchard after bloom, begin treatment.
  • If insect numbers are low in the trees (three or less per ten beats), and lygus bug and calocoris bugs are present in the ground cover, consider treating just the ground cover.
  • If lygus bugs and calocoris bugs move into the trees from drying vegetation, they (as well as phytocoris bugs) can cause damage into early May. California buckeye bug can also be a problem in May if it is established in the orchard or migrates in. By early June or after the shell has hardened, these bugs are no longer damaging.

Due to the variety of small bug species and range of dates they are present, more than one insecticide application may be justified. Be sure to rotate insecticides based on modes of action. Prior to using pyrethroids (Mode-of-action Group 3) for small bugs, also consider whether pyrethroid use is planned for leaffooted bug, stink bugs, or navel orangeworm and plan a resistance management program accordingly.

Common name Amount per acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. PERMETHRIN
  (Pounce 25WP*) 8–16 oz 12 0
  (Ambush 25W*) 12.8–25.6 oz 12 0
  MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Highly toxic to honey bees. Do not apply near aquatic areas; Pounce 25WP and Ambush 25W are restricted-use pesticides because they are highly toxic to fish and aquatic organisms.
 
B. BIFENTHRIN
  (Brigade WSB*) 8–32 oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply near aquatic areas. Brigade WSB is a restricted-use pesticide because it is highly toxic to fish and aquatic organisms.
 
C. CYFLUTHRIN
  (Baythroid XL*) 2–2.4 fl oz 12 14
  MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply near aquatic areas. Baythroid XL is a restricted-use pesticide because it is highly toxic to fish and aquatic organisms.
 
D. LAMBDA-CYHALOTHRIN
  (Warrior II with Zeon Technology*) 1.28–2.56 oz 24 14
  MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply near aquatic areas. Warrior II is a restricted-use pesticide because it is highly toxic to fish and aquatic organisms.
 
E. FENPROPATHRIN
  (Danitol 2.4EC*) 10.66–21.33 fl oz 24 3
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not apply near aquatic areas. Danitol 2.4EC is a restricted-use pesticide because it is highly toxic to fish and aquatic organisms.
 
F. CARBARYL*
  (Sevin 4F) 3–5 qt 12 14
  (Sevin XLR Plus) 3–5 qt 12 14
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: XLR formulation is the least toxic to honey bees when direct application to bees is avoided and the spray residues have dried. Apply from late evening to early morning when bees are not foraging. Usually applied with oil during the dormant season to reduce bugs and other pests (e.g., soft scale) that overwinter on the trees.
 
** 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 safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the R.E.I. exceeds the P.H.I.. The longer of two intervals is the minimum time that must elapse before harvest.
* 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 http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461

Insects and Mites

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

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