How to Manage Pests

UC Pest Management Guidelines

Walnut

Redhumped Caterpillar

Scientific Name: Schizura concinna

(Reviewed 12/07, updated 3/11)

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 treatments 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
Biological control and sprays of Bacillus thuringiensis are acceptable for use 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 treatment is necessary. However, if no parasitism is observed and four or more colonies are found per tree, a treatment is warranted. Insecticide sprays applied for other pests often keep these leaf-eating caterpillars in check. If insecticide treatments are required, all that is generally necessary are localized treatments with a handgun on individual trees when evidence of caterpillars is first observed.

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

 
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.
   
A. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  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. The best timing is to apply before egg hatch. Do not apply more than 0.2 lb a.i. (9 oz)/acre/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 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.
# 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

  • 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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