Cane borers
Oberea bimaculata, Agrilus ruficollis & Hartigia trimaculata
also called Raspberry cane borer, Rednecked cane borer, Rose cane borer
A cane tip that wilts overnight with two neat rings girdled below it, or a swollen gall halfway up. Cut below the damage and the problem is over.
How to know it
Read the damage rather than the insect. Two parallel rings of punctures a centimeter or two apart near the tip of a raspberry cane, with the shoot above them wilting, is the raspberry cane borer. A smooth cigar-shaped swelling in the middle of a cane is the rednecked cane borer. A single round hole in the cut end of a pruned rose stem, with the pith hollowed out below it, is a rose cane borer.
What you'll see
- A cane tip suddenly wilting and hanging over, with the rest of the cane sound.
- Two neat rings of small punctures encircling the cane just below the wilt.
- A smooth cigar-shaped swelling 5–8 cm long in the middle of a raspberry or blackberry cane.
- A round hole in the cut end of a pruned rose cane, with a tunnel running down the pith.
- Canes snapping off at the swelling in wind, or dying back over winter.
Where it comes from
The raspberry cane borer girdles the tip with two rings of punctures and lays an egg between them, so the tip dies and the grub develops in the protected cane below, taking two years to work down to the crown. The rednecked cane borer lays in the bark and its grub spirals under it, causing the gall. Rose cane borers are sawflies and small bees that use the exposed pith of a freshly cut cane.
Raspberries, blackberries and roses everywhere, worst near wild brambles which are the reservoir. Rose cane borers only enter cut ends, so they follow pruning directly.
Dealing with it
- Cut a wilting raspberry tip 15 cm below the lower ring of punctures and bin it — that removes the egg and ends it.
- Cut out and burn any cane with a swelling, all the way back to the ground, in winter.
- Prune a bored rose cane back to sound white pith and seal the cut with a dab of wood glue or wax.
- Do the raspberry inspection weekly through June; a tip caught the same week costs you nothing.
- Do not compost infested canes.
Keeping it out
- Remove wild brambles from the boundary where you can.
- Prune roses to just above a bud rather than leaving a long exposed stub of pith.
- Cut spent raspberry canes out to the ground each year and burn or bin them.
- Keep the row narrow and well thinned so every cane is visible.
- Seal large rose pruning cuts if cane borers are a recurring problem.
What it goes for
Raspberries, blackberries and their hybrids, and roses.
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com