Description of the Pest
Pacific and twospotted mites overwinter as reddish orange mature females in protected places on the tree, in soil, and in decomposing leaf litter on the ground. During warm weather in spring, overwintered females begin feeding on pistachio leaves and ground cover in the orchard. During periods of active feeding twospotted mites have a dark spot on each side of the body. Pacific mites have a second pair of dark spots near the posterior end. Often, however, the spots are barely visible or may coalesce to large dark areas, making it difficult to distinguish the two species.
Colonies develop on the underside of leaves and also on the upper sides when numbers build up. Eggs are spherical and translucent when first laid, becoming opaque soon before hatching. Immature mites molt three times before becoming adults. Spider mites are tiny, less than 1/20 inch (1.3 mm) long. The first stage mites have six legs; later stages and adults have eight legs. These mites reproduce rapidly in hot weather and may become numerous in June or July. They produce many generations a year. If temperature and food supply are favorable, a generation can be completed in 7 days.
Damage
Pacific and twospotted spider mite damage initially appears as a loss of green color on infested leaflets. Continued feeding causes the leaf to develop small, necrotic spots (stippling) with webbing. All mite life stages can be found feeding within this webbing. Low mite levels of 3 to 4 per leaflet are sufficient to cause defoliation in pistachio. Clusters of brown leaves are often the first sign of increasing mite numbers. Defoliation early in the season will greatly reduce nut yield and quality; defoliation late in the season will interfere with harvest.
Areas with somewhat alkaline soils are more likely to have spider mite problems. As in other crops, leaf loss relative to mite levels is enhanced by plant stress from lack of water or high salinity. Greater incidence of damage has been reported with increased pyrethroid use for plant bug control. Many cases involve severe defoliation and a shriveled crop on infested trees.
Management
Spider mites are rarely pests in pistachio orchards, except where natural enemies are absent due to the use of broad-spectrum pesticides or where trees are highly stressed. Tree health and use of selective materials for other pests usually provides adequate spider mite control.
Biological Control
Sixspotted thrips, Scolothrips sexmaculatus, are the most important predators of spider mites in pistachios. Since webspinning spider mite populations develop very slowly on pistachios, thrips often provide effective biological control and insecticides are not needed. Other predators include the spider mite destroyer, Stethorus picipes, and minute pirate bugs.
Cultural Control
Orchard management practices can reduce mite problems.
- Minimize dust by oiling orchard roads and maintaining a ground cover.
- Well-irrigated, vigorous trees sustain less damaged from mite infestations.
- Choose selective pesticides when controlling other pests and avoid pyrethroids, organophosphates, and carbamates until later in the season.
Biological control, cultural controls, and sprays of narrow range oil (mineral oil) are acceptable for use in an organically certified crop.
Monitoring and Treatment Decisions
Monitor from June through August by looking for the presence of spider mites and their predators on leaves. If spider mites are found, wait one week and resample to determine if populations are increasing, decreasing, or staying the same. Spider mite treatments in pistachios are rarely needed, but can be considered if populations and leaf stippling are increasing and defoliation occurs.
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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Zeal | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10B |
2–3 oz | 12 | 28 | — | narrow | moderate | low | low | short | low | low | intermediate | very low | very low | 10/2014 | ||
|
|
FujiMite 5EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
21A |
2–4 pt | 12 | 14 | Apply by ground and use a minimum of 100... | narrow | high | low | low | short | intermediate | low | extra high | very low | low | 10/2014 | ||
|
|
TriTek # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
See label | 4 | 0 | — | — | — | — | — | — | — | — | — | — | — | 10/2014 | ||
|
|
Envidor CA | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
23 |
16–34 oz | 12 | 7 | — | narrow | moderate | low | low | short | low | low | high | low | high | 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.
- # ↩ Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 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
