WSU Extension

Hortsense

Plum, Prune (Fresh) : Peach twig borer
(revision date: 3/10/2017)


Biology
The peach twig borer attacks both shoots and fruit. In the spring, overwintering larvae bore down the center of shoots, causing the tip to wilt or "flag". Each caterpillar can damage several shoots. Later generations of larvae feed on both shoots and fruit. They often burrow into the stem end of young fruit. Pits of infested fruit are often split, with the larvae inside. They may also feed on the fruit surface. The caterpillars are reddish-brown with black heads and yellowish rings on the body. Mature caterpillars are up to 1/2" long. The adult moth is dark gray and about 1/3" long. Apricot, nectarine, and peach may also be attacked. The peach twig borer can be an important pest of peaches, particularly in eastern Washington.
Management Options

Non-Chemical Management
  • Cut out flagging twigs below mined portion. Be sure to kill larvae inside.
  • A tiny wasp parasitizes eggs of the peach twig borer. Avoid use of broad-spectrum insecticides whenever possible to conserve beneficial insects.
  • Overwintering larvae may be found under thin bark in branch crotches. Look for a buildup of chewed bark and frass (excrement).
Select non-chemical management options as your first choice!

Chemical Management

Apply products at bud swell and/or at complete petal fall when later-season larvae bore into twigs, etc. NOTE: Esfenvalerate is toxic to bees. Do not apply products containing esfenvalerate on or near blooming plants. To minimize risk to bees, apply in the evening after bees have stopped foraging for the day. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bug Buster-O [Organic]
    Active ingredient: pyrethrins  |  EPA reg no: 1021-1771-54705
  • Bull's-Eye Bioinsecticide
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-56872
  • ferti-lome Borer, Bagworm, Tent Caterpillar & Leafminer Spray
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-7401
  • Monterey Garden Insect Spray [Organic]
    Active ingredient: spinosad (spinosyn A+D)  |  EPA reg no: 62719-314-54705
  • This list may not include all products registered for this use.
Images
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Caption: Peach twig borer
Photo by: K. Grey
Caption: Peach twig borer larva extracted from damaged apricot
Photo by: M. Bush