Description of the Pest
The pear sawfly, commonly known as pearslug, is not a true slug but resembles one because it exudes a slimy olive green coating over its slug-shaped body; it is actually the larvae of a sawfly. Pearslugs overwinter as pupae. Adult sawflies emerge in spring and are small (about 0.2 inch or 5 mm), shiny black, wasplike, flying insects. Female sawflies lay eggs in the upper surface of leaves, preferring the leaves in the upper portion of the canopy.
Newly hatched larvae are white with a yellowish brown head, turning completely yellow when mature. Soon after they start feeding, however, they cover their bodies with the slimy coating that makes them appear almost black. When mature, the larvae are about 0.5 inch long; the anterior end of the body is wider than the rest of the body. They drop to the soil to pupate. There are two generations a year, with the second generation generally being larger in number than the first and quicker to develop from egg to pupa.
Damage
Pearslugs skeletonize foliage by removing all leaf tissue except the fine network of veins. Damage from both generations can reduce fruit size at maturity. If the second generation causes extensive defoliation of trees, bloom may be reduced the following spring.
Management
Pearslug is often under effective biological control, but in recent years it has become an increasing problem in mating-disruption orchards where broad-spectrum cover sprays are no longer used but populations of natural enemies may not have adequately reestablished.
In backyard trees or organically managed orchards, if a potentially damaging population develops, washing the tree with water from a garden or sprayer hose will dislodge them without disrupting parasites and predators.
Organically Acceptable Methods
Biological control and spray.
Monitoring and Treatment Decisions
In orchards with a history of pear sawfly, start looking for eggs in top shoot samples in April. Continue monitoring top shoots from 20 trees per orchard for larvae throughout the growing season and after harvest. Spot-treat localized infestations in these orchards to prevent them from spreading. For more information regarding sampling for additional pests during the growing season, see SAMPLING DURING FRUIT DEVELOPMENT and POSTHARVEST SURVEY.
| 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. | |||||
| A. | SPINOSAD | ||||
| (Entrust)# | 1 oz/acre | 4 | 7 | ||
| (Success) | 3.5 oz/acre | 4 | 7 | ||
| MODE OF ACTION GROUP NUMBER1: 5 | |||||
| COMMENTS: Do not apply more than 29 oz/acre per year of Success or 9 oz/acre per year of Entrust. Residual efficacy is affected by pH but initial efficacy is not; verify that water pH is greater than 6 and less than 8. | |||||
| B. | METHOXYFENOZIDE | ||||
| (Intrepid 2F) | 6–16 fl oz/acre | 4 | 14 | ||
| MODE OF ACTION GROUP NUMBER1: 18 | |||||
| C. | SPINETORAM | ||||
| (Delegate WG) | 4.5–7 oz/acre | 4 | 7 | ||
| MODE OF ACTION GROUP NUMBER1: 5 | |||||
| COMMENTS: Residual efficacy is affected by pH but initial efficacy is not; verify that water pH is greater than 6 and less than 8. | |||||
| ‡ | 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 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 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). |