Raspberry Cane Borers - What You Can Do This Fall

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

Raspberry cane borer is an occasional pest of raspberries in Minnesota. I recently visited a farm in southeast Minnesota with a moderate infestation. This borer causes the growing tips of raspberry canes to wilt and fall off as the adults pierce holes in the canes for their larvae to enter.

Raspberry growers can scout for this damage in the fall and remove any canes with cane borer damage. Doing so is an effective management strategy to remove most or all of the larvae present.

Raspberry cane borer larvae tunnels seen directly below the puncture holes. Photo: A. Klodd

Recognizing Cane Borers and their Damage

Raspberry cane borer larvae are small, thin and light in color. They can be seen feeding their way down the inside of raspberry canes if you were to cut open an infested cane lengthwise.

The adults are active from late June to early July. They are black beetles with a long and thin body and a patch of yellow between the main part of their body and their head (the thorax).

At this point in the season, it is most important to be able to recognize what their damage looks like so that you can remove the infested canes.

Look for primocanes where the tips wilted and died mid-season.
In some cases, the tips may have fallen off altogether by this point.
At the point where the cane tip died, you should see 1-2 sets of puncture holes. The holes may go all the way around the cane, girdling it.
If you cut into the cane slightly below the puncture holes, the cane should contain a hollow tunnel where the larvae has been feeding.
The infested canes will be stunted and short because their apical growth was stalled mid-season.
Red flag: If a cane is completely dead from the base level, that could be due to a number of things including diseases; at that point you should consult the Plant Disease Clinic about submitting a sample for diagnosis.

Two sets of puncture holes girdling the primocane, created by adult raspberry cane borer. Photo: University of Kentucky.

Know their Life Cycle in Order to Manage Them

Start scouting for adult beetles on the plants in mid-June and continue through mid-July.

From late June through early July, the adults lay eggs on the young, new canes, about 6 inches from their tips. After laying the eggs, they puncture a set of small holes around the perimeter of the cane. This puncture damage is what actually causes the top of the cane to wilt. The beetles do this so their larvae have an easy entry into the cane.

Then, the larvae emerge from their eggs in July, burrow into the canes, and eat their way down for a few inches. Eventually, they continue feeding down the rest of the cane and overwinter at the base of the cane near the roots. The next spring, they become adult beetles, emerge from the soil, and begin the lifecycle over again.

Managing Raspberry Cane Borer Without Insecticides

The main way to manage cane borers takes place during the summer and does not involve insecticides. When you first see a cane that is wilting or dead near the top, look for those puncture holes mentioned above. If they are present, cut the cane about 2 inches below the holes. Then remove those cuttings from the field and burn them to kill the larvae and eggs.

Even though we are moving into the dormant season, you can still cut the infested canes now; this will likely remove some or most of the larvae, because the larvae spend their first winter in the canes. It is considered acceptable to just cut the cane 2 inches below the puncture holes if you want to harvest from the floricane next season, or to remove the whole cane.

Insecticides are usually unnecessary for cane borer control. The problem is rarely bad enough for insecticides to be economically beneficial. In other words, think about whether the cost of application is worth what you will save in terms of plant health or yield. In most cases, the answer is no, because the damage is minor and infested canes still produce fruit from lower laterals. Furthermore, this application usually doesn't coincide with the timing of the first SWD insecticide application, because it is done prior to fruit ripening.

After considering this, if you do decide to apply an insecticide in the case of a severe infestation:

Only two insecticides are labeled and recommended for rednecked cane borer (Note: different species than raspberry cane borer) in our region. The Midwest Fruit Management Guide does not list any insecticides for Raspberry cane borer. The two insecticides listed for rednecked cane borer are Admire Pro and JMS Stylet Oil. Apply one or both of these insecticides as soon as you to kill the adult beetles in late June when you begin to see them. Start looking for them in mid-June so that you do not miss this window. Try to avoid spraying during bloom to reduce impact on pollinators.

Admire Pro: Soil-applied to kill emerging adults. 10.5-14 fluid ounces per acre.
JMS Stylet Oil: Foliar-applied weekly as long as adults are active. 0.5-1.0 gallons per acre.