Cane borer and crown borers in raspberries

There are a number of insect pests that attack the canes and crowns of raspberries in Ontario. Distinguishing these can be confusing but is important for control. One way to different between these pests is to note where the injury occurs: raspberry crown borer can be found at the base of the plant in the crown, red-necked cane borer tends to attack the cane 1-3 feet above the ground, and the raspberry cane borer attacks primocane tips, and then travels down to the base of the cane.

Raspberry cane borer

This pest is a slender, dark coloured beetle, about 12 mm long, with antennae as long as its body. Larvae are white, cylindrical and legless. Adult females chew two zipper-like rings around the tips of raspberry primocanes and lay an egg between the punctures. The tip wilts above the point of injury and eventually dries up (Figure 1). The beetles are active in late June, July and August. Primocanes wilt immediately after egg-laying occurs. The larvae tunnel down the canes and overwinter, continuing to the base of the cane the following spring. They usually kill the fruiting cane before the fruit matures and overwinter another winter at the base of the dead cane.

Growers should examine canes frequently in June and July for injury. Cut off wilted tips below lower ring as they appear and burn them. Admire 240 F has been recently registered for control of raspberry cane borer. This product is very toxic to bees and must not be applied before or during bloom on raspberries.

Fig 1: Damage from raspberry cane borer on primocane tip

Raspberry crown borer

The adult is a clear-winged moth with a wingspan of 2.5-3.0 cm. The yellow bands across its black abdomen cause it to resemble a yellow jacket wasp (Figure 2). The adult moth is active in July and August and lays eggs on raspberry leaves. The larvae hatch and travel down the cane and overwinter in a small cell at its base. The following spring they burrow at the base of the cane, in larger roots and in the crown. Mature larvae are up to 2.5 cm in length, cream coloured with brown heads and obvious legs. Larvae spend two years in the crown and root area before they emerge as adults (Figure 3). Around harvest time of the second summer, they pupate and emerge from the crown.

Canes infested with raspberry crown borer wither and die or are stunted with small fruit. Canes that grow out of infested crowns can sometimes be pulled or tugged away from the crown to reveal borer damage and insect frass. Eventually, primocanes become so few in number that the planting dies out.

The control strategy for crown borer includes diazinon or azinphosmethyl insecticides are targeted at the base of the cane in fall or early spring before the larvae tunnel in. Treatment is required for two years to break the cycle of this pest. Use of azinphosmethyl has been phased out and this is one of the last uses allowed on fruit crops. Regulators and researchers are actively searching for alternatives to these organophosphate insecticides. Please see OMAFRA publication #360 for details.

Fig 2: Raspberry crown borer adult moth

Fig 3: Crown borer larvae in crown

Red-necked cane borer

This pest, also known as the rose-stem girdler, is seen occasionally in raspberries in Ontario. The adult beetle is a small (6 mm) dark metallic beetle with a flat head and reddish coloured band just behind the head (Figure 4). The beetle emerges from fruiting canes in late June and early July. Eggs are laid on the lower half of the primocanes. Larvae tunnel in a spiral fashion around the cane (Figure 5). The first few spirals under the bark result in a swelling or gall. The larvae continue to tunnel up or down the cane in the pith. Infested canes may wilt or dry up and often break off at the gall (Figure 6). Injury is most frequently observed in late summer, fall or winter when infested canes break off about two to three feet above the ground. To control red-necked cane borer, prune out and remove infested canes before spring. Admire 240F has been recently registered for control of this pest.

Fig 4: Red-necked cane borer adult

Fig 5: Spiral shaped tunnel from red-necked cane borer on cane

Fig 6: Damage and swelling on cane from red-necked cane borer