How to Manage Pests

UC Pest Management Guidelines


Webspinning Spider Mites

Scientific Names:
Pacific spider mite: Tetranychus pacificus
Twospotted spider mite: Tetranychus urticae

(Reviewed 11/09, updated 11/09, pesticides updated 9/15)

In this Guideline:


These two spider mites have similar life histories and are controlled in the same manner. Overwintering female mites are red- or orange-colored and are found under rough bark, in ground litter, and on winter weeds. Adult males do not overwinter and are smaller than females. During the growing season their color ranges from yellow to green to black depending on age and host food. Both species have dark spots on their bodies.

Eggs are laid on the foliage. Immature mites molt three times. Early in the season mites are found in lower to central areas of the tree. The mites reproduce rapidly during warm weather between June and September. During favorable conditions, mites develop within 7 days with eight to ten generations per season.


Mites damage foliage by sucking cell contents from leaves. The damage begins with leaf stippling. Leaves can turn yellow and drop off. High populations cover tree terminals with webbing. Crop reduction shows up the year after damage occurs.


In many cases biological control keeps spider mites under control. Miticides may be necessary in some orchards in summer, but only when mite populations reach damaging levels, which often occurs after pesticides have been used that disrupt natural enemies. Keeping cherry orchards well irrigated during summer will help reduce the likelihood of mite outbreaks that are severe enough to warrant treatment.

Biological Control

Several species play a large role in mite control, including the western predatory mite (Galendromus [=Metaseiulus] occidentalis), sixspotted thrips, spider mite destroyer, brown lacewing, and green lacewing. The western predatory mite is the most reliable mite predator. It is the same size as spider mites, but lacks spots and ranges in color from cream to amber red. This predator maintains good control unless the proportion of leaves with spider mites is higher than the proportion of leaves with predatory mites.

Cultural Control

Reduce dusty conditions in orchards by oiling or watering roadways and maintaining a ground cover. Prevent water stress, as this condition results in higher mite densities and intensified damage.

Organically Acceptable Methods

Biological and cultural controls and oil sprays are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions

Regular monitoring will help determine if biological control is keeping spider mites under control or if treatments are needed. Begin monitoring leaves for mites in March. From March through May, monitor every other week; monitor weekly from May through August. Check trees at random throughout the orchard, and separately sample trees along dusty roads, areas of the orchard that are stressed, and areas that have had mite problems in the past. Sample at least 15 leaves from each tree, taking leaves from inside the canopy on the lower part of the tree. Record the number of leaves with pest mites and the number of leaves with predators. If the number of leaves with predators is nearly the same as the number with pest mites, no treatment is needed. Return in a week or so and sample again. If the number of leaves with pest mites is increasing and the number with predators is not, then treat. Presence of a large number of mite eggs is an indication that the population is increasing.

Spot treatments may be sufficient because heavy infestations usually start in dusty or stressed areas of the orchard. Use materials that are least harmful to natural enemies. Spray oils can be used as long as trees are not stressed, but oils are not effective on mite infestations that have developed heavy webbing. Oil sprays reduce mite populations about 50% in two weeks; so monitor mite numbers again two weeks after treatment to see if an additional spray is needed.

If treatment is needed early in the season and predators are present, you can use below-label rates of a miticide to reduce the pest population and help preserve predators. Treatments are not needed after the first of September; mite populations decline naturally at this time.

Common name Amount to use** REI‡ PHI‡
(Example trade name) (conc.) (dilute)
(hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
A. NARROW RANGE OIL Label rates See label 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  . . . PLUS . . .(optional)
  (Acramite 50WS) 0.75–1 lb/acre 12 3
  COMMENTS: May be applied only once per crop season. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
  . . . or . . .
  (Envidor 2SC) 16–18 fl oz/acre 12 7
  COMMENTS: May be applied only once per crop season.
  . . . or . . .
  (Onager) 12–24 oz/acre 12 7
  COMMENTS: May be applied only once per crop season.
  . . . or . . .
  (Zeal) 2–3 oz/acre 12 7
  COMMENTS: Apply once per crop season to nonbearing trees.
  . . . or . . .
  (Apollo SC) 2–8 oz/acre 12 21
  COMMENTS: This material is more effective in the early part of the year; apply after sampling indicates pest mites are increasing but before significant damage or webbing is present. Kills eggs and young larval stages. Good coverage is a must; use a minimum of 50 gal water/acre for concentrate and a maximum of 400 gal water/acre for dilute. To delay development of resistance, use only once per season.
  (Omite 30WS) 5–6 lb/acre 48 See comments
  COMMENTS: Postharvest use only. Do not apply less than 40 days after or 30 days before an oil application.
C. NARROW RANGE OIL# Label rates See label 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Do not apply within 30 days of a propargite application. Be sure that trees are not water-stressed or injury may result. Not all oils are organically acceptable; be sure to check individual products.
** For concentrate applications, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute applications, amount is per 100 gal water to be applied in 300–400 gal water/acre, according to label.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 ("un" = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at
# Acceptable for use on organically grown produce.




[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440

Insects and Mites

J. A. Grant, UC Cooperative Extension, San Joaquin County
J. L. Caprile, UC Cooperative Extension, Contra Costa County
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
K. M. Daane, Kearney Agricultural Center, Parlier

Acknowledgment for contributions to Insects and Mites:
J. Colyn, Mid-Valley Ag. Services
M. Devencenzi, Devencenzi Ag. Pest Mgmt. and Research
P. McKenzie, Mid-Valley Ag. Services

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   Contact webmaster.