How to Manage Pests

UC Pest Management Guidelines

Walnut

Redhumped Caterpillar

Scientific Name: Schizura concinna

(Reviewed 7/17, updated 7/17)

In this Guideline:


Description of the Pest

The redhumped caterpillar is easily recognized because of its striking appearance: the main body color is yellow and is marked by longitudinal reddish and white stripes. The head is bright red, and the fourth abdominal segment is red and enlarged. Redhumped caterpillars pass the winter as full-grown larvae in cocoons on the ground. In early summer, moths lay egg masses on the under surface of leaves. Eggs hatch into larvae that begin feeding on leaves. There are at least three generations each year.

Damage

Redhumped caterpillars skeletonize leaves, leaving behind only leaf veins. They form no webbing on the leaves.

Management

A number of natural enemies attack redhumped caterpillar and often prevent it from becoming a destructive pest. Isolated infestations on small trees may be pruned out and destroyed. Occasional insecticide applications may be required on young trees.

Biological Control

Among the parasites that help prevent redhumped caterpillars from becoming destructive pests are two parasitic wasps, Hyposoter fugitivus and a species of Apanteles. The larvae of both parasites develop inside the caterpillar and pupate on the leaf surface in groups of silken cocoons. General predators include spiders, lacewings, bigeyed bugs, and damsel bugs.

Organically Acceptable Methods

Use biological control and sprays of Bacillus thuringiensis in an organically certified crop.

Monitoring and Treatment Decisions

Monitor for redhumped caterpillar during nut and shoot development.

Generally, control of redhumped caterpillar is only necessary on young trees. If 80 to 90% of the larvae in the second brood are parasitized, no insecticide application is necessary. However, if no parasitism is observed and four or more colonies are found per tree, an insecticide application is warranted.

Insecticide sprays applied for other pests often keep these leaf-eating caterpillars in check. If insecticide applications are required, all that is generally necessary are localized sprays with a handgun on individual trees when evidence of caterpillars is first observed.

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. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: 11A
  COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.
 
B. CHLORANTRANILIPROLE
  (Altacor) 3–4.5 oz 4 10
  MODE-OF-ACTION GROUP NUMBER1: 28
  COMMENTS: Larvicide. Do not apply more than 0.2 lb a.i. (9 oz)/acre per year. Do not make more than four applications per year.  To reduce the development of resistance do not make more than three consecutive applications of any group 28 insecticides (anthranilic diamide) per generation per season.
 
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 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.
# 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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