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Raspberry Insect Problems

Raspberry Cane Borers

By: Sandy Feather 2009
Penn State Extension


Q. I think my fall raspberries have raspberry cane borers and I'm wondering how to break the cycle. I've been cutting the canes to the ground and disposing of them in the trash. The reason I suspect raspberry cane borers is because the canes look healthy with berries starting, which suddenly wither and then die. The fruit doesn't ripen. Canes appear to have galls near the soil surface and when they are cut open, there is often a worm resembling some sort of larva.

A. A variety of cane borers make their living on raspberries. Raspberry cane borer (Oberea bimaculata) and red-necked cane borer (Agrilus ruficollis) are the two most common in our area. You're already doing the best thing to control both insects - Prune out and dispose of the infested canes. It is also advisable to eliminate wild brambles growing within 500 feet of your raspberries.


Raspberry Borer description

Raspberry cane borer adults are black beetles with a bright orange mark right behind the head. Two or three black spots dot the orange area. These long-horned beetles are slender, about one-half inch long, and their antennae are roughly as long as their bodies. Adults become active in late spring, and females lay their eggs singly on the new growth at the tip of the cane. They make a double row of punctures around the stem that are three-quarters to one inch apart, and then use a needle-like ovipositor to insert an egg between the rows deep into the pith or center of the stem. The tips whither and die because the double row of punctures cut off the flow of water and nutrients to infested tips.
  

raspberry cane
Raspberry canes

  
Larvae begin tunneling through the pith toward the base of affected canes as soon as they hatch, but entomologists have observed conflicting behavior. Some have observed the larvae make it to the base of the cane in a single growing season, while others have observed them move just an inch or two below the double row of punctures during the first season, and only make it to the base of the cane the following year. The white, legless larvae grow to three-quarters of an inch long. Their tunneling activity weakens infested canes, and often causes them to die before the fruit they bear has a chance to mature. Control options stress pruning out wilted tips several inches below the double row of punctures by midsummer, and pruning out old, unproductive canes anytime.


Red-necked Cane Borer

The red-necked cane borer takes its common name comes from the reddish area behind the adult insect's head. These otherwise black beetles are active from late May until early August. They have much shorter antennae than raspberry cane borer adults, and grow to about one-quarter inch long.

 

Adults can be seen feeding on raspberry foliage during the day. After feeding for several days, females lay their eggs on the raspberry canes' new growth. These hatch in four to twenty-four days. Newly hatched larvae tunnel into the cane where they make winding tunnels under the bark as they work their way into the pith. Their activity results in irregular swellings or galls that range from one to three inches long. The bark often splits above these galls, which can be found anywhere along the cane, although it is quite common to find them at ground level.


Life Cycle

The larvae grow to about three-quarters of an inch long, and are creamy white and legless, with a pair of dark "pincers" on the last abdominal segment. Infested canes often break off at these swellings, and/or are weakened so much that they die. Larvae overwinter inside the canes, pupate the following spring, and hatch out as adults in late May or early June. The adults chew a "D"-shaped exit hole to emerge from the cane, a characteristic shared by the related bronze birch borer and emerald ash borer. The primary control for red-necked cane borer is pruning out infested stems any time from late fall until early spring. Live larvae are not usually found in the galls.

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