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UC Pest Management Guidelines


Leaffooted bug adult.

Pistachio

Leaffooted Plant Bugs

Scientific names: Leptoglossus clypealis, Leptoglossus occidentalis

(Reviewed 2/07, updated 2/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Adult leaffooted plant bugs are relatively large insects, 0.75 to 1 inch in length. Both 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.

Leaffooted bugs overwinter as adults, typically in aggregations located in protected areas, such as in woodpiles, barns, under the bark of eucalyptus, cypress, or juniper trees. These pests can also overwinter in the orchard in plant debris, pump houses, or cracks along the tree trunk. In April and 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 seeds. 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/October to April/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.

Leaffooted plant bugs typically damage entire clusters.

MANAGEMENT

Leaffooted bugs normally do not appear in orchards until late in the season (August and September). 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 temperature extremes and an egg parasitoid (Gryon pennsylvanicum). However, these natural controls can not be relied upon if there is a large overwintering population. 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
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
Sample for nymphs using a beating tray; adult will either fly away or cling to the tree and not drop.

Hold the 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. If the bugs are present (e.g., 1 bug per 15 or 20 beats), particularly early in the season, treatment may be necessary. There are no reliable sampling methods for adults in spring. Instead, look for small, black nuts in clusters or on the ground in late April to early May for the first indication of bug presence in the orchard.

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

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
Consider impact on natural enemies and honey bees as well as information relating to environmental impact.
 
A. PERMETHRIN*
  (Pounce) 3.2EC 8–16 oz 12 0
  (Ambush) 25WP 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 and 1.6 lb a.i./acre/season for 3.2 EC information.
 
B. BIFENTHRIN*
  (Brigade) WSB 8–32 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 3
 
C. CYFLUTHRIN*
  (Baythroid XL) 2–2.4 fl oz 12 14
  MODE OF ACTION GROUP NUMBER1: 3
 
** 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 REI exceeds the PHI. 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
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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