How to Manage Pests

UC Pest Management Guidelines

Walnut

European Red Mite

Scientific Name: Panonychus ulmi

(Reviewed 7/17, updated 7/17)

In this Guideline:


Description of the Pest

The European red mite overwinters in the egg stage on twigs and branches. The red orange eggs have a long spike that is visible with a hand lens. Eggs hatch in early spring when the walnuts leaf out. Immature mites are bright red; adult females have a brick red, globular body with four rows of long, curved hairs arising from white dorsal spots. Newly molted mites may appear greenish. Adult males are brownish and smaller than the females. European red mites produce little or no webbing.

Usually red mite numbers build slowly during spring and do not become damaging until summer. They have multiple generations each season.

Damage

European red mites feed on the cell contents of leaf tissue. Initially, the feeding causes light stippling of the leaves. Prolonged feeding by high numbers of mites gradually gives leaves a bronzed appearance. Feeding by European red mite does not result in leaf drop, as does feeding by webspinning mites, but severe repeated bronzing of leaves for several years can reduce nut yields significantly. Damage by European red mite is generally rare, but damage is more common in cooler coastal areas than in hot, inland orchards.

Management

European red mite can serve as a food source for predatory mites early in the season and help numbers of beneficial mites develop to levels sufficient to assist in controlling webspinning spider mites. A pesticide application is not recommended for low to moderate numbers of this mite.

Biological Control

In low numbers, the European red mite can be beneficial by providing a food source for predatory mites in spring. These predators can build to numbers that may be sufficient to control webspinning mites, which appear later in the season. The other predators described in the section on webspinning mites also attack European red mite.

Organically Acceptable Methods

Biological control and sprays of narrow range oils can be used in an organically certified crop. Caution should be taken when applying oils in walnuts to avoid injuring trees (see narrow range oil comments in the table below).

Monitoring and Treatment Decisions

Look for European red mites during the dormant period by examining leaf and growth scars on twigs for clusters of red eggs. To combine monitoring for European red mites and other pests see DORMANT MONITORING. A dilute, delayed-dormant oil spray may aid in the control of European red mite. (Do not apply oils to walnut during dormant season.)

During spring, look for buildup of European red mite numbers and stippling or bronzing on leaves, especially in the shady, central parts of trees. You can check for European red mites when sampling for webspinning mites. Because damage by this mite is rare, no damage threshold levels are available to determine when to treat. Avoid spraying low to moderate levels of European red mites because they can be important in maintaining predators of other mites.

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.
 
Oils are not recommended for use during the dormant season on walnut trees.
 
A. NARROW RANGE OIL# 4 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Provides short-term control. Must be applied in a dilute application of at least 300 gal/acre. In most areas, oils can be applied to walnuts during the delayed-dormant period (as buds begin to swell) and in summer. Do not apply after husk split. However to avoid injury, the trees must not have suffered from a lack of adequate soil moisture or other stressing factor (insects, disease damage, etc.) at any time during the year and the temperature must not exceed 90°F at or shortly after time of application. If in doubt, check with your farm advisor. In any case, do not apply oils to walnuts during the dormant season or between bud break and shoot elongation. Check with certifier to determine which products are organically acceptable.
 
B. CYFLUMETOFEN
  (Nealta) 13.7 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 25
  COMMENTS: To prevent resistance, do not make more than one Nealta application before using an effective miticide with a different mode of action.
   
C. FENBUTATIN-OXIDE*
  (Vendex 50WP) 2 lb 0.5 lb 48 14
  MODE-OF-ACTION GROUP NUMBER1: 12B
  COMMENTS: Do not apply more than twice per season.
 
D. BIFENAZATE
  (Acramite 50WS) 0.75–1 lb 12 14
  (Vigilant 4SC) 16–24 fl oz 12 14
  MODE-OF-ACTION GROUP NUMBER1: 20D
  COMMENTS: Do not apply more than once per season.
 
E. CLOFENTEZINE
  (Apollo SC) 2–4 oz 0.5–1 oz 12 30
  MODE-OF-ACTION GROUP NUMBER1: 10A
  COMMENTS: Is effective against mites that are resistant to propargite. Apply after sampling indicates pest mites are increasing but before significant damage is present. Kills eggs and young larval stages. 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.
   
F. HEXYTHIAZOX
  (Onager) 12–24 oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 10A
  COMMENTS: Do not apply more than once per year.
   
G. ABAMECTIN*
  (Agri-Mek SC) 2.25–4.25 fl oz 0.5–1 fl oz 12 21
  MODE-OF-ACTION GROUP NUMBER1: 6
  COMMENTS: Use in combination with a horticultural spray oil at a minimum of 1 gal/acre. Is effective against mites that are resistant to propargite. Apply after sampling indicates pest mites are increasing, but before significant damage is present. A locally systemic material that is most effective if applied before July when foliage is still young and tender enough to absorb it. To delay development of resistance, use only once per season. Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations. Regulations affect use for the San Joaquin Valley from May 1 to October 31, 2017. Review the Department of Pesticide Regulation's updated fact sheet.
 
H. PROPARGITE*
  (Omite 30WS) 4–6 lb 1.5 lb See label 21
  MODE-OF-ACTION GROUP NUMBER1: 12C
  COMMENTS: Propargite cannot be used more than twice per season, nor can animals be grazed on vegetation under treated trees. Propargite should never be used within 14 days before or after the application of any oil, or phytotoxicity may occur. These rates are lower than the manufacturer's label rate.
 
I. ETOXAZOLE
  (Zeal) 2–3 oz 12 28
  MODE-OF-ACTION GROUP NUMBER1: 25
  COMMENTS: Kills eggs and larval stages. Best used when mite numbers are low.
 
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 concentrate application, use the amount given in 80 to 100 gal water/acre, or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300 to 500 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 these two intervals is the minimum time that must elapse before harvest may occur.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown crops.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Insects and Mites

J. A. Grant, UC Cooperative Extension, San Joaquin County
J. K. Hasey, UC Cooperative Extension, Sutter, Yuba, and Colusa counties
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
E. J. Symmes, UC IPM Program, Butte County
S. J. Seybold, Entomology, UC Davis (walnut twig beetle)
R. M. Bostock, Plant Pathology, UC Davis (walnut twig beetle)

Acknowledgment for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Research and Extension Center, Parlier (Emeritus)
L. C. Hendricks, UC Cooperative Extension, Merced County (Emeritus)
W. H. Olson, UC Cooperative Extension, Butte County (Emeritus)
C. Pickel, UC IPM Program, Sutter and Yuba counties (Emeritus)
G. S. Sibbett, UC Cooperative Extension, Tulare County (Emeritus)
D. Light, USDA, Albany, CA (Emeritus)(Codling Moth)

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