How to Manage Pests

UC Pest Management Guidelines

Pistachio

Leaffooted Plant Bugs

Scientific names: Leptoglossus zonatus, Leptoglossus clypealis, Leptoglossus occidentalis

(Reviewed 10/14, updated 10/14)

In this Guideline:


DESCRIPTION OF THE PESTS

Adult leaffooted plant bugs are relatively large insects, 3/4 to 1 inch in length. All three species are similar in appearance; they are brown in color with a narrow white band across the back, although this band is less distinct in L. occidentalis. The head appears pointed, and the hind legs have an expanded area that superficially resembles a leaf, hence its name. Leptoglossus zonatus can be distinguished by the presence of two yellow spots on the pronotum. Leptoglossus clypealis does not have the yellow spots and has a long pointed clypeus that points forward at the front of the head.

Leaffooted bugs overwinter as adults, typically in aggregations located in protected areas, such as in woodpiles, barns, under the bark of eucalyptus, citrus, palm, cypress, or juniper trees. These pests can also overwinter in the orchard in plant debris, pump houses, or cracks along the tree trunk. From late March through May, adults disperse to find food sources. These insects are primarily seed feeders and, once in the orchard, they will feed directly on the developing nuts or on ground vegetation. Adults are strong flyers and can disperse from overwintering sites and quickly move into and within the orchard. Overwintered adults are long-lived, from September or October to April or May. Their eggs are laid in spring usually on leaves, twigs, and nuts; some Leptoglossus species deposit over 200 eggs. After nymphs emerge from a round hole on top of the egg, they develop into adults in 6 to 8 weeks. Because the adults are long-lived and can lay eggs over an extended period, the population can consist of all life stages by late June. There may be 2 to 3 generations per year, depending on temperatures and food sources.

DAMAGE

These insects are capable of causing two types of damage. The first type (epicarp lesion) is produced early in the season and is similar to that caused by other plant bugs. Nuts damaged during or shortly after bloom blacken and drop. If nuts are damaged during the period in which they are enlarging, the damaged tissue turns brown and necrotic and the outside will often become sunken and appear almost water soaked. The internal lesions often develop a white, netted appearance in the shell tissue, with no deep pitting.

After shell hardening in June, leaffooted bugs may cause a second type of damage called kernel necrosis, which is not obvious on the shell. Externally all that is evident is a brown pinpoint mark. With kernel necrosis, the nutmeat is darkened, often develops a sunken or distorted area, and may have an off-flavor. If this occurs when humidity is high, a fungal breakdown of the nut causes it to turn slimy. This is referred to as stigmatomycosis.

Leaffooted plant bugs typically damage most of the nuts in an attacked cluster.

MANAGEMENT

Leaffooted bugs typically first appear in orchards starting in April. However, if they overwinter in or near pistachio, they may be found earlier, usually feeding on nut clusters, and at this time they can cause considerable nut drop when their populations densities are high.

Biological Control

In most years leaffooted bug populations are controlled by natural mortality from extremely cold winter temperatures and an egg parasitoid (Gryon pennsylvanicum). However, these natural controls cannot be relied upon if there is a large overwintering population typically following a mild, dry winter. This is especially true during the critical spring period as the egg parasitoid will only impact the adult's offspring, and it is the overwintered adult that will cause most damage.

Cultural Control

During the season there are no cultural controls known to affect the density of the leaffooted bug or the damage it causes to pistachios. However, cultural controls such as cleaning debris from near the orchard may help reduce overwintering populations.

Monitoring and Treatment Decisions

During dormant and delayed dormant tree pruning, check for leaffooted plant bug when looking for Botryosphaeria cankers.

Starting in April monitor weekly through nut development.

  1. Sample trees for leaffooted plant bug nymphs with a beating tray as done for small plant and stink bugs.
    1. Hold a beating tray under nut clusters while striking the limb sharply three times with a lightweight club (immature leaffooted bugs will drop onto the tray and can be easily examined; adults will either fly away or cling to the tree and not drop.)
    2. Examine bugs that drop onto the tray. If nymphs are present (e.g., 1 bug per 15 or 20 beats), particularly early in the season, treatment may be necessary.
    3. The best time to take beat samples is in the morning when bugs are less active and are easier to examine; one exception is for the flight of adult leaffooted bugs when the tree is shaken.
  2. Also look for leaffooted plant bug and stink bug egg masses on the leaves and fruit.
  3. There are no reliable sampling methods for adults in spring. Instead, look for adult leaffooted plant bugs migrating in from overwintering sites and small black nuts in clusters or on the ground in late April to early May.
  4. If black nuts are found, cut them open to confirm damage (black lesions inside the hull).

Leaffooted bugs are capable of transmitting some pistachio diseases, such as stigmatomycosis and Botryosphaeria panicle and shoot blight, making control of these pests important.

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. 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.
 
B. 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.
 
C. LAMBDA-CYHALOTHRIN
  (Warrior II with Zeon*, etc.) 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.
 
D. PERMETHRIN*
  (Pounce 25WP*) 8–16 oz 12 0
  (Ambush 25W*) 12.8–25.6 oz 12 0
  MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: May be used on either early or late developing populations. Do not apply more than 0.8 lb a.i./acre/season for 25W formulation. 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.
 
** 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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