Raspberries: Cane Borer (Girdler) and Flat-headed Cane Borers

Raspberry Cane Borer

The raspberry cane borer (Oberea bimaculata), is sometimes referred to as raspberry cane girdler. This beetle lays an egg in a d-shaped hole cut near the tip of primocanes.

Close-up of raspberry stem section with oval-shaped depression cut into surface. One side of the depression is curved, while the other side is more straight, resembling the letter D. The depression is one-third of the width of the stem. An elongated, beige-tan egg is visible in the center of the depression. The egg is almost as long as the depression but narrower in width.
Raspberry cane borer (Oberea bimaculata) egg in raspberry primocane stem.

The adult then girdles the cane both above and below the egg.

Close-up of raspberry cane covered in puncture marks. Tissue surrounding puncture marks is brown. Puncture marks are arranged in 2 neat, horizontal lines across the entire stem. One larger hole is placed between the horizontally-girdled region.
Girdling of fruiting cane and egg deposition site, symptomatic of raspberry cane borer activity.

This causes the primocane tips to wilt, and in some instances, to break.

A raspberry floricane appears snapped in half approximately 3-5 inches from the tip.
Removing and disposing of the broken-off tip of a floricane can prevent the next generation of insects from hatching.

If tips are not removed below the girdle, then eggs will hatch and larvae will burrow down the cane into the crown.

Flat-headed Cane Borers

There are multiple species of flat-headed cane borers. Two prominent pests of raspberry are the Rednecked Cane Borer (Agrilus ruficollis) and the Bronze Cane Borer (Agrilus rubicola). These beetles do not girdle canes as does the Raspberry Cane Borer (Oberea bimaculata).

Adults of both insects feed along leaf edges. Females insert eggs into young canes. Borer larva, or grubs, hatch and tunnel inside the cane while feeding. This causes a symmetrical gall or swelling to form.

Close-up of raspberry stem with vertical strips of damaged tissue, where the stem appears to have cracked from being stretched internally. Below the area with strips of damage, there is a spherical hole the size of a large pinhead.
Flat-headed cane borer (Agrilus rubicola or A. ruficollis) tunnel entrance and cane damage.

Canes are weakened, wilting above the swelling, and sometimes breaking off.

Raspberry cane with girdling from multiple horizontal lines. The outer surface of the cane is split and cracked, as if it became swollen and the skin split. Cane is torn off above the girdle marks.

Yellowing of upper portion of fruiting cane; lower portion of cane remains unaffected.

Raspberry cane with one ripe raspberry at tip. Leaves on stem are lighter in color than on neighboring canes. Some leaves are bronzed at edges. Leaves at base of cane are healthy and dark green.

Removal of leaves reveals borer swelling.

Raspberry cane with stripped leaves revealing a pale green stem with an irregular, elongated patch of purple-red stem. The discolored section is slightly swollen and curves along the cane, being approximately 3-4 inches in length.
Flat-headed cane borers, such as Agrilus ruficollis and Agrilus cuprescens, cause a discolored swelling on raspberry canes.

 

Beetle on leaf. Beetle has elongated black abdomen with vertical ridges. Beetle head is rust-colored with a flattened front. Beetle is approximately as long as one penny, but more narrow in shape.
The Rednecked Cane Borer (Agrilus ruficollis) adult.
Close-up of raspberry cane with small, straight, greenish-yellow larva on lower portion of cane. Larva is marked by faint horizontal stripes that split the body into numerous segments, and a small dark head with no antenna. Raspberry cane has old and fresh vertical splits and cracks along the surface. Old cracks are browned and marked with scar tissue. New crack is wider and does not yet have brown tissue surrounding the damage.
Exposed rednecked cane borer (Agrilus ruficollis) larva visible below cane swelling.

More information:

Use these resources if you need additional help with diagnosis and to find solutions to your problem.