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 feed in groups on leaves. There are at least three generations each year in Northern California.
Redhumped caterpillars generally skeletonize leaves, leaving behind only leaf veins. They do not web leaves.
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.
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.
On small trees, cut out and destroy infested twigs.
Organically Acceptable Methods
Use cultural and biological control, as well as sprays of Bacillus thuringiensis, and the Entrust formulation of spinosad on organically grown apricots.
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 Bacillus thuringiensis are effective against the larvae.
|Common name||Amount to use**||REI‡||PHI‡|
|(Example trade name)||(conc.)||(dilute)||(hours)||(days)|
|Not all registered pesticides are listed. 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. Always read the label of the product being used.|
|(Entrust)#||1.25–2.5 oz||0.42–0.83 oz||4||14|
|(Success)||4–8 fl oz||1.3–2.7 fl oz||4||14|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: This product is toxic to bees for 3 hours following treatment; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. Apply in the late evening after bees have stopped foraging. Do not apply more than 29 fl oz/acre per year of Success or 9 oz/acre per year of Entrust.|
|B.||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.|
|(Intrepid 2F)||8–16 fl oz||2–4 fl oz||4||14|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|COMMENTS: Do not apply more than 16 fl oz/acre per application or more than 64 fl oz/acre per season.|
|(Altacor)||3–4.5 oz||0.75–1.125 oz||4||10|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|COMMENTS: Do not apply more than 9 oz/acre per year or make more than three applications a year. Do not apply with less than 100 or more than 200 gallons water/acre.|
|(Diazinon 50W)||1 lb/100 gal||4 days||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. Do not apply more than 4 lbs. product per application.|
|**||For concentrate applications, 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 400 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 two intervals is the minimum time that must elapse before harvest.|
|#||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).|
|*||Permit required from county agricultural commissioner for purchase or use.|