How to Manage Pests

UC Pest Management Guidelines

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 spring and 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 plum orchards in the Central Valley. 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, which forms a single pupal case that is white with a black band around the middle, and a species of Apanteles, which forms a fluffy white mass of pupal cases. 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
Biological and cultural control and Bacillus thuringiensis (Bt) sprays are acceptable for use in an organically certified crop.

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. 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 to Use**		R.E.I.+	P.H.I.+
(trade name)		(conc.)	(dilute)	(hours)	(days)
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees, impact of timing on beneficials, and environmental impact Not all registered pesticides are listed. Always read label of product being used.
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.
**	For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, according to label; for concentrate applications, use 80–100 gal water/acre, or lower if the label allows.
+	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.
#	Acceptable for use on organically grown produce.
—	Not recommended or not on label.
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/.

PUBLICATION

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

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