Description of the Pest
The eggs of the raspberry horntail, a wood wasp, are pearly white and oblong, with a curved point at one end. Mature larvae are white and cylindrical, with dark heads and a short spine on the tail end. They have three pairs of legs, no prolegs, and attain a length of up to 1 inch (2.5 cm). The adult wasps, which are seldom seen, vary from 0.5 to 0.75 inch (12–18 mm) in length. The females are marked with bright yellow and black; the males are mostly black.
Damage
Beginning in April, female horntails insert their eggs just under the epidermis of both blackberry and raspberry canes, about 2 inches (5 cm) below the tips. A few days later eggs hatch into very small larvae that spirally girdle the tips of the canes and cause wilting. In most cases the cane recovers, although they remain slightly crooked. The cane is weak in the area of the crook and often breaks at this point during pruning and training. Larvae later feed throughout the terminal portion of the cane, which often causes dieback.When mature, they burrow down the pith in canes and spend the winter in silk-lined cells in the burrows. In spring they pupate and adults emerge through a round hole cut in the sides of the canes. In some locations horntails may have two generations per year.
Management
Low populations of horntails do not cause serious damage. Removing and destroying infested canes when wilting becomes apparent will remove the larvae from the patch and help reduce the total population. Also, larvae may be parasitized by small wasps in the ichneumonid family. These parasitic wasps occur naturally and are not commercially available for release. Use insecticides for control only when three actively wilting canes are counted per 100 feet of row. Begin monitoring in April. In order to avoid killing pollinating honeybees, do not spray insecticides during bloom.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (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. | ||||
| A. | CARBARYL* | |||
| (Sevin XLR Plus) | 1–2 qt | 12 | 7 | |
| MODE-OF-ACTION GROUP NUMBER1: 1A | ||||
| COMMENTS: Carbaryl sprays will give good control of horntails, but may cause a buildup of spider mites. Apply in 100 gal water in a full coverage spray. Highly toxic to honey bees; do not apply if crops or weeds are in bloom. The XLR Plus formulation is less hazardous to honey bees when direct application to bees is avoided and the spray residues have dried. Apply from late evening to early morning when bees are not foraging. | ||||
| ‡ | 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. |
| * | Permit required from county agricultural commissioner for purchase or use. |
| 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). |