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Pile of frass at entrance of peach twig borer hibernaculum.

Monitor Hibernacula

Peach twig borers overwinter in hibernacula, which are sawdust or frass-covered cells bored under the thin bark of limb crotches or bark cracks. Monitor hibernacula only in orchards that did not receive a dormant treatment for peach twig borer.

Starting at popcorn, examine at least 10 hibernacula each week using the procedure below. Most hibernacula are commonly found in the crotch of 2- to 3-year-old wood.

  1. Use a hand lens to find tiny piles of reddish frass that mark the entrance of the hibernaculum.
  2. Cut out small wedges of bark around the reddish frass.
  3. Pinch each wedge of bark to open the hibernaculum, and use a hand lens to look for a peach twig borer larva. If the larva is not present, it has emerged.

Make the first treatment application when 20 to 40% of the larvae have emerged and the second application 7 to 10 days later or when emergence has reached 80 to 100%. If emergence is spread out, a third spray may be needed when emergence finally reaches 80 to 100% because of the relatively short time that Bt residues are present at effective levels following application.

Names link to more information on identification and management.

Click on photos to enlarge
Pile of frass at entrance of peach twig borer hibernaculum.
Peach twig borer hibernacula
Identification tip: Hibernacula are most commonly found in the crotch of 2- or 3-year-old wood. Look for tiny piles of reddish frass.
Cutting a wedge of bark including a hibernaculum to monitor peach twig borer emergence.
Small wedge around hibernacula
Identification tip: Cut out small wedges of bark around the small reddish piles of frass that mark the entrance of the hibernanculum.
Pinching open wedge of bark with peach twig borer hibernaculum to reveal larva inside.
Examining hibernacula
Identification tip: Pinch open a wedge of bark with peach twig borer hibernaculum to see if larva has emerged yet.
Mature larva of peach twig borer.
Peach twig borer larva
Identification tip: Larvae are small, brown caterpillars with white inter-segmental bands and a black head capsule.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

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