Description of the Pest
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.
Psallus vaccinicola (there is no common name) is the least common of these small plant bugs. 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.
- Sample the trees with a beating tray.
- Hold the tray under nut clusters while striking the limb sharply three times with a lightweight club.
- Examine bugs that drop onto the tray.
- The best time to take beat samples is in the morning when bugs are less active and easier to examine.
- Sample the cover crop and surrounding vegetation with a sweep net for lygus bug and calocoris bug.
- Phytocoris bugs can also be monitored with pheromone traps, but research has not been done to correlate trap catches with economic injury.
- 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.
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 | ||
| Sevin XLR Plus | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
1A |
3–5 qt | 12 | 14 | XLR formulation is the least toxic to ho... | broad | low | high | high | long | low | low | intermediate | low | low | 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 | ||
|
|
Danitol 2.4 EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
10.66–21.33 fl oz | 24 | 3 | Do not apply near aquatic areas. Danitol... | narrow | — | — | — | short | high | high | 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 | Highly toxic to honey bees. Do not apply... | 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.
- * a Permit required from county agricultural commissioner for purchase or use.
- 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
