How to Manage Pests

UC Pest Management Guidelines

Adult twospotted spider mite, Tetranychus urticae.

Pear

Webspinning Spider Mites

Scientific names:
Twospotted spider mite: Tetranychus urticae
Pacific spider mite: Tetranychus pacificus
McDaniel spider mite: Tetranychus mcdanieli

(Reviewed 11/12 , updated 11/12 )

In this Guideline:


DESCRIPTION OF THE PESTS

Adult female mites are yellow in color. Feeding mites have dark spots on either side of the body. The tiny, spherical, colorless to light-straw-colored eggs are distributed over the infested area. Overwintering females are orange, and hibernate under bark scales on the tree and in trash on the ground. They move up the tree in late March and April, feeding on leaves. Rapid reproduction occurs in hot, dry weather and the infestation peaks in July and August.

DAMAGE

Webspinning mites produce a characteristic blackening of pear leaves when they feed. Pear trees can tolerate fewer webspinning mites than European red mites. Usually two to three mites feeding near the midrib of a leaf produce black areas from the midrib to the margin. This blackening may appear even after mites have been controlled, especially if a period of hot weather follows the spray application. High mite populations may cause defoliation. Severe defoliation can stunt fruit and may cause the trees to bloom in fall, thus reducing next year's crop. However, if defoliation is limited to water sprouts in the top or interior of the tree, it will not adversely affect the crop or tree.

MANAGEMENT

Webspinning spider mites are typically most abundant during the hot summer months, especially in dusty and water-stressed areas of the orchard. Orchards with high predator-to-pest-mite ratios and good dust and water-stress management may not need treatment, especially orchards using codling moth mating disruption. Monitor regularly. When treatment is needed, choose products least disruptive to biological control.

Biological Control

The western predatory mite, Galendromus (=Metaseiulus) occidentalis, is an excellent predator of webspinning mites. A ratio of one predator to 10 twospotted mites is necessary for the predators to keep control of the leaf-feeding mites. Use lower rates of miticides to minimize destruction of predators and allow some spider mites to survive. Biological control by predatory mites can also be encouraged by suppressing spider mites with oil added to one or more codling moth sprays to improve predator-prey ratios. Western predatory mite is most effective in sprayed orchards and may not compete as well in organic orchards where there are many other natural enemies of mites.

Cultural Control

Orchards with cover crops and sprinkler irrigation have been most suitable for an IPM mite program because these practices minimize dust. Do not allow the cover crop to become dry as this will cause webspinning mites to disperse to trees. Do not allow cover crops to grow into trees forming bridges for the mites to move from the cover crop to the trees. Low-growing grasses host fewer webspinning spider mites than broadleaf weeds such as morningglory, tall grasses such as johnsongrass, and broadleaf cover crops such as clover. Mow or apply herbicides at a time during the year that will not trigger migration of webspinning mites into the trees.

Organically Acceptable Methods

Biological and cultural controls and sprays of certain oil products are organically acceptable.

Monitoring and Treatment Decisions

Begin sampling for webspinning spider mites when pears turn down. Collect 5 spur leaves at eye height from one scaffold branch from each of 20 marked trees that have been established as representative trees in a block. Examine 5 leaves from each shoot with a hand lens (10 to 14X) and count both European red mites (eggs, nymphs, and adults) and webspinning mites (nymphs and adults only). As a general guideline, if no mites are found in the sample, you can wait 3 weeks to resample. If there is less than one mite per leaf, resample in 2 weeks, and if there is one mite per leaf, take your next sample in 1 week.

Once a week during the summer months, also check 5 leaves on 20 top shoots for presence of webspinning mites. For more information regarding sampling, see SAMPLING DURING FRUIT DEVELOPMENT.

Postharvest monitoring

Following harvest, check 5 leaves on 20 top shoots for webspinning spider mites. For more information about monitoring at this time, see POSTHARVEST SURVEY.

The following mite thresholds are for Bartlett pears and include all stages of European red mite and webspinning mite nymphs and adults. Bosc pears are more susceptible to spider mites and should be treated at lower thresholds. Asian pear and other varieties usually tolerate more mites than French pear varieties, making biological and cultural controls easier to implement.

CONTROL ACTION THRESHOLDS
Plant stage Mites/100 leaves Action
Turn down pear to harvest 1–50 mites Treat with oil.
50+ mites Add miticide to the oil spray.
Postharvest, early districts only 51–100 mites Treat with oil. If predaceous mites are present at 1:10 ratio, spraying may not be needed.

 

Common name Amount to use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute)
(hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
PETAL FALL TO HARVEST
A. NARROW RANGE OIL 4 gal 1 gal 4 0
  MODE OF ACTION: Contact, including smothering and barrier effects.
  . . . PLUS . . .
  ABAMECTIN*
  (Agri-Mek 0.15EC) 10–20 oz 2.5–5 fl oz 12 28
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: Apply early when leaf tissue is tender and good coverage is easier. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
 
B. BIFENAZATE
  (Acramite 50WS) 1 lb 0.25 lb 12 7
  MODE OF ACTION GROUP NUMBER1: 25
  COMMENTS: Only one application per crop per year. New material and there is little experience in California regarding efficacy and effect on beneficials. Most effective with use of a silicone spreader.
 
C. ACEQUINOCYL
  (Kanemite 15SC) 21–31 fl oz 5.25–7.75 fl oz 12 14
  MODE OF ACTION GROUP NUMBER1: 20B
  COMMENTS: There is little experience in California regarding efficacy. Most effective with use of a silicone spreader.
 
D. ETOXAZOLE
  (Zeal) 2–3 oz 0.5–0.75 oz 12 14
  MODE OF ACTION GROUP NUMBER1: 10B
  COMMENTS: Preliminary research indicates etoxazole has an effect on the reproductive capacity of predatory mites. Most effective with use of a silicone spreader.
 
E. SPIRODICLOFEN
  (Envidor 2SC) 16–18 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 23
  COMMENTS: Do not apply to blooming plants, including fruit trees and broadleaf weeds.
 
F. FENPYROXIMATE
  (FujiMite 5EC) 2 pt 0.5 pt 12 14
  MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Most effective with use of a silicone spreader. Toxic to predatory mites.
 
G. CLOFENTEZINE
  (Apollo) 4 oz 1 oz 12 21
  MODE OF ACTION GROUP NUMBER1: 10A
  COMMENTS: Kills eggs. Need to apply early, before monitoring indicates a need; use in orchards where European red mite is a chronic pest. Good coverage is a must; use a minimum of 50 gal water/acre for concentrate sprays and a maximum of 400 gal water/acre for dilute. To delay development of resistance, use only once per season.
 
H. HEXYTHIAZOX
  (Savey 50WP) Low- to mid-label rate 12 28
  MODE OF ACTION GROUP NUMBER1: 10B
  COMMENTS: Kills eggs. Need to apply early, before monitoring indicates a need. Apply only once per growing season.
 
POSTHARVEST
 
A. NARROW RANGE OIL# 4 gal 1 gal 4 0
  MODE OF ACTION: Contact, including smothering and barrier effects.
  COMMENTS: Apply this spray according to monitoring guidelines. Check with your certifier to determine which products are organically acceptable.
 
** Dilute rate is the rate per 100 gal water; use 400 gal solution/acre. Apply concentrate in 80–100 gal water/acre, or less if the label allows.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at www.irac-online.org.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455

Insects and Mites

L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County
R. B. Elkins, UC Cooperative Extension, Lake County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
C. Ingels, UC Cooperative Extension, Sacramento County
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
P. W. Weddle, Weddle, Hansen & Associates
R. Hansen, Weddle, Hansen & Associates
P. Chevalier, United Ag Products, Ukiah
M. Hooper, Ag Unlimited, Lakeport
B. Knispel, Pest Control Adviser, Upper Lake
T. Lidyoff, Purity Products, Healdsburg
G. McCosker, Harvey Lyman Agservices, Walnut Grove
B. Oldham, Ag Unlimited, Ukiah
J. Sisevich, AgroTech, Kelseyville (retired)
D. Smith, Western Farm Service, Walnut Grove
B. Zoller, The Pear Doctor, Inc., Kelseyville

Top of page


Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2014 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   /PMG/r603400211.html revised: April 25, 2014. Contact webmaster.