Raspberry cane borer

About

A long, slender black beetle with a patch of yellow behind its head. Its larva tunnels down raspberry canes over two years.

Spotting it

Damage

New cane tips suddenly wilt in early summer. Look just below the wilt for two rings of punctures about half an inch apart; below them the cane is hollowed out.

How to find it early

From mid-June to mid-July, look for wilted, drooping cane tips and the telltale double ring of punctures.

When

Early to midsummer (wilted tips); larvae feed inside canes year-round.

Life cycle

In late June and early July, females girdle a new cane with two rings of punctures 4 to 6 inches below the tip and lay an egg there. The larva tunnels down the cane its first year and into the crown the second, so the life cycle takes two years.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Cut out wilted tips below the rings By hand

   During the season, cut infested canes at least 2 inches below the lower ring of punctures, before the larva moves down. In fall, cut a few inches below the holes or remove the whole cane.

   Destroy the cuttings or take them out of the garden; do not leave them in the patch.

2. Usually not needed Conventional spray

   UMN says the damage rarely justifies spraying; pruning is the main control.

Plants it goes after

Black raspberry (blackcap), Dewberry, Raspberry, Salmonberry

Pressure by region

UMN calls it an occasional pest in Minnesota. No other regional source was found, so every rating except the Midwest's is an estimate.

Ratings come from extension sources where available; some are estimates, as noted above.