How to Manage Pests

UC Pest Management Guidelines

Walnut

European Red Mite

Scientific Name: Panonychus ulmi

(Reviewed 12/07, updated 4/09)

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. Usually red mite populations build slowly during spring and do not become damaging until summer. They have multiple generations each season. European red mites produce little or no webbing.

DAMAGE

European red mites feed on the cell contents of leaf tissue. Initially, the feeding causes light stippling of the leaves. Prolonged feeding by a heavy population will gradually give 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 it has a tendency to be more abundant 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 populations of these beneficial mites develop to levels sufficient to assist in controlling webspinning spider mites. Treatment is not recommended for low to moderate population levels of this mite.

Biological Control
In low numbers, the European red mite can be beneficial by providing a food source for the western predatory mite, Galendromus (=Metaseiulus) occidentalis, in spring. This predator can build its population 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.

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 treatment may aid control of European red mite. (Do not apply oils to walnut during dormant season.) During spring, look for buildup of European red mite populations 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 treating low to moderate levels of European red mites because they can be important in maintaining predators of other mites.

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 label of product being used.
         
CAUTION: 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. PROPARGITE      
  (Omite) 30W 4–6 lb 1.5 lb 7 days 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.
         
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
  MODE OF ACTION GROUP NUMBER1: 25
  COMMENTS: Do not apply more than once per season.
         
E. ABAMECTIN*      
  (Agri-Mek) 0.75­1 lb 12 21
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: Use in combination with a horticultural spray oil at a minimum of 1 gal per acre. Is effective against mites that are resistant to propargite. Apply after sampling indicates pest mites are increasing but before significant damage or webbing 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.
   
F. 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 or webbing is present. Kills eggs and young larval stages. Good coverage is a must; use a minimum of 50 gal water per acre for concentrate sprays and a maximum of 400 gal water per acre for dilute. To delay development of resistance, use only once per season.
   
G. HEXYTHIAZOX        
  (Onager) 12–24 oz 12 28
  MODE OF ACTION GROUP NUMBER1: 10B
  COMMENTS: Do not apply more than once per year.
   
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 http://www.irac-online.org/.
** For concentrate application, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300–500 gal water/acre, according to label.
+ 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 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.
Not recommended or not on label.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Insects and Mites

  • C. Pickel, UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
  • J. A. Grant, UC Cooperative Extension, San Joaquin County
  • W. J. Bentley, UC IPM Program/Kearney Agricultural Center, Parlier
  • J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
  • W. W. Coates, UC Cooperative Extension, San Benito County
  • R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to Insects and Mites:
  • W. H. Olson, UC Cooperative Extension, Butte County
  • L. C. Hendricks, UC Cooperative Extension, Merced County
  • G. S. Sibbett, UC Cooperative Extension, Tulare County

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