Blueberry Stem Borers

If you grow blueberries, be on the lookout for these longhorned beetles.
 
No, we’re not talking about Texas longhorns. Blueberry stem borers (Oberea myops) are in a family of narrow beetles with long antennae (Cerambycidae). Also known as rhododendron borers and azalea borers, they are close cousins to raspberry cane borers.
 
Adult blueberry stem borers are slightly over one-half of an inch long (15mm), light orangish brown, with long black antennae and two black dots just behind the head, on the pronotum. Larvae can be one inch long (25mm) and yellowish.
 
Females lay individual eggs just under the bark and then mark the area by girdling the stem above and below the egg. This damage causes the stem tip to turn brown in early summer.
 
After hatching, larvae burrow lower into the stem, creating an increasingly larger tunnel where they will live and feed for two or three years. Larval feeding weakens the plant, causing wilting, stem damage, and branch loss.
 
If you look closely, you may be able to see tiny holes in the stem where larvae push out light-colored frass (poop) that looks like tiny segmented pieces of sawdust. Unlike currant borers, peach twig borers, and squash vine borers, blueberry stem borer larvae frass holes are oriented upward, so the use of a wire to stab the larvae tends to be ineffective because they stay safely below those holes.
 
Adult blueberry stem borers tend to feed on the underside of leaves, especially on the midvein, causing calluses and leaf curling. While that feeding damage is minimal, you can use it as a tool to monitor your plants.
 
Protected inside your blueberry plants, blueberry stem borer larvae are not affected by insecticides. While you can spray for adults, this is generally not worth the effort. The best control tool is your pruners.

Pruning your blueberry bushes to keep them free of old, damaged, or rubbing stems is your best defense against blueberry stem borers.