Description of the Pest
Cankerworm larvae have three pairs of prolegs. They are greenish above, with three narrow, whitish stripes and one yellow stripe along the side of the body; underparts are light green. Cankerworms frequently stand on the posterior pair of prolegs in such a way that they resemble a small twig. Fall cankerworms pass the winter in the egg stage. Fall caterpillars hatch and feed on leaves in spring and summer, then pupate and develop into moths in fall. There is one generation per year.
Damage
The larvae are primarily leaf feeders, tending to skeletonize leaves. Occasionally they feed on young fruit by biting deep holes, which later heal, but leave large scarred depressions similar to the injury caused by green fruitworms.
Management
Insecticide sprays applied for other pests often keep these leaf-eating caterpillars in check.
Cultural Control
On small trees, cut out and destroy infested twigs.
Organically Acceptable Methods
Cultural control and Bacillus thuringiensis (Bt) sprays are acceptable for use on organically certified produce.
Treatment Decisions
Bloom or postbloom treatments of Bacillus thuringiensis will control this pest when larvae are present. The Bt program used for peach twig borer control reduces cankerworm damage.
| 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. | |||||
| BLOOM and POSTBLOOM | |||||
| 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 (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. |
| — | Not recommended or not on label. |
| 1 | Rotate insecticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |