Description of the Pest
(View photos of pest mites and damage online.)
Twospotted and Pacific spider mites are not easily distinguished: both have two black spots on yellow to green bodies. In fall they turn orange red before overwintering as adult females in protected spaces under bark and in weeds. The twospotted spider mite is most common in the Sacramento Valley and the Pacific spider mite in the San Joaquin Valley. When weeds dry in spring, the mites move to trees first feeding on lower leaves towards the middle of the tree (scaffold crotch area). They eventually become distributed over the entire tree. There are many overlapping generations each summer, with eggs being laid in a fine webbing on the undersurface of leaves. During very hot weather, mite populations can double in a week, with 8 to 10 generations per season.
Damage
Webspinning spider mites are the most damaging mites to prunes. Spider mites feed by sucking the contents out of leaf cells. This leaf damage reduces tree vigor and fruit size. Defoliation because of spider mite damage often results in sunburn of the tree and fruit. Leaf injury caused by spider mites begins as a mottling and browning of leaves. Defoliation usually follows if control measures are not initiated. Both mites produce abundant webbing on both sides of the leaves.
Management
In many cases biological control keeps spider mites below economically damaging levels. Application of miticides may be necessary in some orchards in summer, but only when mite numbers reach damaging levels, which often occurs after pesticides that disrupt natural enemies have been used. Use timed searches from June 1 to July 15 to assess the need for treatment.
Biological Control
(View natural enemy photos online.)
Biological mite control can be very effective. Several species play an important role in mite control, including western predatory mite (Galendromus [= Metaseiulus] occidentalis), sixspotted thrips, the spider mite destroyer (Stethorus sp.) and minute pirate bugs (Orius sp.). Understanding different mite predator behaviors are important to successful spider mite biological control.
Six spotted thrips is an extremely good mite predator. In recent years, the sixspotted thrips has become the most common insect predator of spider mites in some orchard crops such as almond. and. It is highly mobile and both nymphs and adults feed on spider mites. However, movement of sixspotted thrips into orchards can be unpredictable and sometimes does not occur until mites have already exceeded treatment thresholds. If sixspotted thrips is present in an orchard, avoid using pyrethroid or spinosyn insecticides or miticides containing abamectin to preserve their presence and maximize biological control. Six spotted thrips also feed on predatory mites.
The most widespread predatory mite is the western predatory mite. It is about the same size as spider mites, but the western predatory mite lacks spots and its color ranges from cream to amber red. It often can be observed moving quickly over the underside of leaf surfaces in search of spider mites. This predator maintains good control, unless the proportion of leaves with spider mites is higher than the proportion with predatory mites.
Predators will typically control webspinning mites if presence-absence sampling indicates equivalent numbers of leaves with predators and with webspinning mites. When predator mites are present, but are not controlling the spider mites, a lower-than-label rate of a selective miticide may be applied to create a more balanced ratio (i.e., a 1:1 ratio of one leaf with a predatory mite for every leaf with a webspinning mite). If predatory mites are present in an orchard, choose a miticide with reduced toxicity to predatory mites. See the Relative Toxicities of Insecticides and Miticides table for a list of pesticides used on prune and their toxicity to the western predatory mite.
Predatory mites can be purchased from insectaries and released to augment natural populations of predatory mites. Before releases, be sure that insecticide residues have sufficiently broken down to allow the survival of predatory mites. For example, research has shown that some pyrethroid insecticides can be highly toxic to predatory mites for several months to more than a year after application. In some cases, predatory mites from insectaries have been reared from stocks with tolerance to one or more pesticides, such as organophosphates and carbaryl, enabling survival in orchards if residues are present. Keep purchased mites cool when they are received from the insectary and release them as soon as possible. Release predatory mites when spider mites are present (to allow predatory mites to feed) but well before treatment thresholds are reached.
Predatory mite releases are not advised in areas where sixspotted thrips are present, since these predatory thrips are known to eat both spider mites and predatory mites. For more detailed information on predatory mite releases, see Natural Enemy Releases for Biological Control of Crop Pests.
Cultural Control
Vigorously growing trees are much more tolerant to mite attack than stressed trees. Maintain trees with optimum irrigation and fertilization. Reduce dusty conditions in orchards by oiling or watering roads and by maintaining a ground cover. Do not allow the ground cover to dry in mid-summer or mites will move up into the trees.
Organically Acceptable Methods
Use biological and cultural control, mineral oil sprays, and the release of predatory mites in a certified organic crop.
Monitoring and Treatment Decisions
Soon after bloom, start looking for spider mites and predatory mites on the first leaves emerging from scaffolds. Use this information to map out areas of concern for future monitoring in the fruit development season.
Take weekly samples using the timed search method below, from June 1 (or earlier in drought years) to July 15 until the treatment threshold has been reached and a treatment has been applied. Record observations on a monitoring form (PDF). If a treatment is applied on or after July 15, monitoring is no longer necessary. Continue to monitor untreated orchards until harvest.
How to Monitor
- In each orchard up to 40 acres, conduct a 5-minute search in 2 separate areas of the orchard, for a total sampling time of 10 minutes.
- For each 5-minute search, examine at least 2 to 3 leaves on 10 trees. Note presence or absence of spider mites or predators. Sample leaves from both inside and outside the tree.
- If mite population is spotty, continue to do two 5-minute searches throughout the summer. If you determine the mite population is consistent throughout orchard, one 5-minute search is adequate.
- Keep records of sample results on the monitoring form.
- Use the guidelines below to determine need for treatment.
Mite Ratings (percent of leaves with one or more mites)
- low (1–20%) = an occasional mite on occasional leaf; hard to find.
- low/moderate (21–39%) = mites easier to find but no colonies or webbing and few eggs.
- moderate (40–60%) = some leaves without mites, other leaves with small colonies; eggs easy to find but very little webbing.
- moderate/high (61–79%) = mites on most leaves, colonies with eggs, and webbing on some leaves.
- high (80–100%) = many mites on most leaves; eggs and webbing abundant.
Predator Ratings
- low = hard to find; less than one predator per six leaves (only a few leaves will have predators).
- moderate = easier to find; one predator per three leaves (about half the leaves will have predators).
- high = one or more predators per leaf (most leaves will have predators).
Treatment Decisions (Treat if the rating from at least on 5-minute search indicates):
- low/moderate mite rating with low/moderate predator rating, or
- moderate/high mite rating with moderate/high predator rating
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(fish) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Galendromus occidentalis # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
NA |
— | — | — | Predatory mites can be released early in... | — | — | — | — | — | — | — | — | — | — | — | 12/2025 | |
|
|
Agri-Mek SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
6 |
2.25–4.25 fl oz | 12 | 21 | — | broad | moderate | low | moderate/high | moderate | high | low | extra high | low | intermediate | 12/2025 | ||
|
|
Vigilant 4SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
20D |
12–16 fl oz | 12 | 3 | Relatively safe for beneficial predatory... | narrow | low | low | low | short | — | — | — | — | — | 12/2025 | ||
|
|
Nealta | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
25A |
13.7 fl oz | 12 | 7 | Contact miticide that targets all stages... | — | — | — | — | — | very low | low | intermediate | very low | very low | 12/2025 | ||
|
|
Zeal | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10B |
2–3 oz | 12 | 7 | Affects both predatory and pest mites. A... | narrow | high 13 | low | — | short | low | low | intermediate | very low | very low | 12/2025 | ||
|
|
Magister SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
21A |
32–36 fl oz | 12 | 3 | — | narrow | — | — | — | moderate | low | low | high | very low | low | 12/2025 | ||
|
|
Vendex 50WP | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
12B |
2 lb | 48 | 14 | Fenbutatin oxide appears to be most effe... | narrow | low | low | low | short | high | intermediate | extra high | very low | low | 12/2025 | ||
|
|
FujiMite SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
21A |
2 pt | 12 | 7 | Contact toxin to juveniles and adults wi... | narrow | high | low | low | very long | intermediate | low | extra high | very low | low | 12/2025 | ||
|
|
Onager | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10A |
12–24 oz | 12 | 7 | Apply after bloom, before adult mite num... | narrow | low | low | low | short | low | low | intermediate | low | intermediate | 12/2025 | ||
|
|
Omni Supreme # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
4–6 gal | 12 | — | COMMENTS: Narrow range oil used alone wi... | broad | low | low | low | none to short | very low | low | very low | very low | very low | 12/2025 | ||
|
|
Nexter | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
21A |
8.8–10.67 oz | 12 | 7 | This is not as selective as other mitici... | broad | high | moderate | — | short | intermediate | low | extra high | very low | very low | 12/2025 | ||
|
|
Envidor CA | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
23 |
16–18 fl oz | 12 | 7 | Contact pesticide that targets all stage... | narrow | low | — | — | — | low | low | high | low | high | 12/2025 |
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 b 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.
- 13 ↩ Does not kill adults but sterilizes females.
Important Links
UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
F.J.A. Niederholzer, UC Cooperative Extension Sutter/Yuba counties
Acknowledgement for Contributions to Invertebrates
W.O. Reil (emeritus), UC Cooperative Extension Solano and Yolo counties
C. Pickel (emeritus), UC IPM and UC Cooperative Extension Sutter and Yuba counties
W.H. Olson, UC Cooperative Extension Butte County
F.G. Zalom (emeritus), Entomology, UC Davis
R.P. Buchner (emeritus), UC Cooperative Extension Tehama County
R. Krueger, USDA, ARS, Riverside
