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UC Pest Management Guidelines


Redhumped caterpillar larva.

Apricot

Redhumped Caterpillar

Scientific name: Schizura concinna

(Reviewed 11/07, updated 11/07)

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 undersides of leaves. Eggs hatch into larvae that begin feeding on leaves. There are at least three generations each year in northern California.

DAMAGE

Redhumped caterpillars generally skeletonize leaves, leaving behind only leaf veins. They do not web leaves.

MANAGEMENT

Redhumped caterpillar can be a pest of apricot orchards in the Central Valley; it is not usually found in Central Coast orchards. Biological control and pruning is often sufficient to manage the pest; use the monitoring guidelines below to determine need for treatment.

Biological Control
A number of natural enemies attack redhumped caterpillars, frequently preventing them from becoming destructive pests. Most common are two parasitic wasps, Hyposoter fugitivus, and a species of Cotesia (Apanteles). Several general predators, including spiders, lacewings, bigeyed bugs, and damsel bugs occasionally feed on caterpillar eggs and small larvae.

Cultural Control
On small trees, cut out and destroy infested twigs.

Organically Acceptable Methods
Cultural and biological control as well as sprays of Bacillus thuringiensis and the Entrust formulation of spinosad.

Monitoring and Treatment Decisions
Begin looking for redhumped caterpillars in May, when eggs or larvae of the first generation may be present. Check trees throughout the orchard, looking at the undersides of leaves for egg masses or groups of small larvae. Skeletonized leaves that turn brown may indicate the presence of redhumped caterpillars. If you find larvae of the first generation, do not treat. Prune out and destroy localized infestations.

Monitor again in July for second-generation larvae and for the presence of parasites before you make a treatment decision. Look for parasite pupae among larval colonies. Caterpillar larvae parasitized by Cotesia have numerous small, white, fluffy tubes protruding from their bodies. Caterpillars parasitized by Hyposoter have a thin, gray pupa attached by a tiny cord to their desiccating bodies.

If 80% or more of the larval population is parasitized no treatment is needed. If parasitization is very low, prune out and destroy infestations or treat infested trees. Infestations tend to be very localized; so spot treatments usually suffice. Formulations of Bt are effective against the larvae.

Common name Amount/Acre 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.
 
A. SPINOSAD
  (Entrust)# 1.71–2.5 oz 0.43–0.6 oz 4 14
  (Success) 6–8 fl oz 1.5–2 fl oz 4 14
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: This product is toxic to bees for 3 hours following treatment; apply in the late evening after bees have stopped foraging. Do not apply more than 29 fl oz/acre/year of Success or 9 oz/acre/year of Entrust.
 
B. 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.
 
C. METHOXYFENOZIDE
  (Intrepid) 2F 8–16 fl oz 2–4 fl oz 4 7
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: Do not apply more than 16 fl oz/acre/application or more than 64 fl oz/acre/season.
 
D. DIAZINON* 50WP 3 lb 1 lb 24 21
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Avoid drift and tailwater runoff into surface waters. Where apricots are grown adjacent to waterways, do not use this material.
 
 
**  For concentrate applications, 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 300-400 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 two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.
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 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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Apricot
UC ANR Publication 3433
Insects and Mites
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
K. A. Kelley, UC Cooperative Extension, Stanislaus County
J. L. Caprile, UC Cooperative Extension, Contra Costa County
Acknowledgment for contributions to Insects and Mites:
L. C. Hendricks, UC Cooperative Extension, Merced County

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