Raspberry Cane Borer

The adult raspberry cane borer (Oberea bimaculata ) appears in June. It is a slender black beetle about 1/2″ long. 

Raspberry Cane Borer Adult

(Image: Michigan State University)

How to recognize it and its’ presence

This pest is a slender, dark coloured beetle, about 12 mm long, with antennae as long as its body. It can be recognized by the yellow band near its head and its long antennae. 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 cane tip wilts above the point of injury and eventually dries up and dies.

The beetle cuts 2 rings around the stem about 1″ apart and those two rings appear 4″ – 8″ below the shoot tip. An egg is laid between the rings and the top of the cane wilts and dies.

Raspberry Cane Borer Larva

(Image: Maine.gov)

When the egg hatches the larva bores into the pith and feeds until it overwinters just below the point of girdling. The next season the larva bores down to the base of the cane and overwinters at or below ground level. The larva pupate in the spring and the adults emerge.

The Upside!

The cane borer usually only attacks a few plants out of the patch each year, so if you pay attention you should be able to control it before the borer does any great damage to your whole patch. Keep a close eye on your patch in June and July, look frequently for signs of the tips wilting.

The best control is accomplished by looking for and cutting off the affected canes a few inches below the point of girdling.

Do not compost or reuse them for anything, the best plan is to burn the infected canes and be sure the pest is out of your garden. You can see in the image below the two dark rings around the cane in the background of the wilted leaves. (Image: Michigan State University)

Activity

Raspberry Cane Borer Wilt

(Image: Michigan State University)

The beetles are active in late June, July and August. Primocanes wilt immediately after egg-laying occurs. At the end of summer the larvae tunnel down the canes and overwinter near the base inside the cane. They over winter and the adults emerge again the next June.

Their life cycle usually takes 2 years but sometimes they complete it in one year.

Pesticide

There isn’t usually a need for pesticide if you have a consistent watch going on for wilting cane tips and disposing of them completely.

If the infestation is severe, pesticide sprays are targeted at the adults at the stage right before the flowers open in the spring.  

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