Description of the Pest
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.
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.
- Sample trees for leaffooted plant bug nymphs with a beating tray as done for small plant and stink bugs.
- 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.)
- 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.
- 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.
- Also look for leaffooted plant bug and stink bug egg masses on the leaves and fruit.
- 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.
- 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.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
Brigade WSB | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
8–32 oz | 12 | 7 | Do not apply near aquatic areas. Brigade... | broad | high | high | high | long | intermediate | low | extra high | very low | intermediate | 10/2014 | ||
|
|
Baythroid XL | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
2–2.4 fl oz | 12 | 14 | Do not apply near aquatic areas. Baythro... | broad | high | high | high | moderate | intermediate | intermediate | extra high | very low | very low | 10/2014 | ||
|
|
Warrior II | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
1.28–2.56 oz | 24 | 14 | Do not apply near aquatic areas. Warrior... | broad | high | high | high | moderate | intermediate | low | extra high | low | high | 10/2014 | ||
|
|
Pounce 25 WP | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
8–16 oz | 12 | 0 | May be used on either early or late deve... | broad | low | high | high | long | intermediate | low | extra high | very low | intermediate | 10/2014 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
R.H. Beede (emeritus), UC Cooperative Extension Kings County
W.J. Bentley (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
K.M. Daane, Kearney Agricultural Research and Extension Center, Parlier
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
Acknowledgement for Contributions to Invertebrates
R.E. Rice, Kearney Agricultural Research and Extension Center, Parlier
