Each year, we look forward to a generous harvest of raspberries. From our small patch of plants, we generally are able to prepare and store around 60 half-pint jars of jam for the coming year. However, this year, to date, we have only prepared 4 half pints.
To say that this has been a very bad year for raspberries would be an understatement. Our neighbors and friends have been reporting the same. While the berry patch looks healthy and vibrant at first view, more is going on below the surface.
The first signs of trouble appeared in early summer, back in June. Some of the tops of the raspberry canes began to wilt and die off. The problem appeared to accelerate even while at the same time the plants continued to grow and develop berries. What was going on? A neighbor, knowledgeable in plants, led us to the answer. The Raspberry Cane Borer. This native beetle evidently is very common, attacking the plants along the cane by drilling two rings of tiny holes into the plant about 1/2 to 1 inch apart. Between those two rings, the female beetle lays an egg that later in the summer season develops into a larvae. The larvae then makes its way down the cane towards the soil and the roots by hollowing out a tunnel in the cane, thus causing the destruction or severe weakening of the plant. Ultimately, some sections of the cane give way and fall off, leaving a blackened scar where a cane branch used to be.
What to do about this? There are a number of helpful resources online (found most easily by an online search under the topic of "raspberry borer") that will help you to identify the species of borer and the remedy for stopping the beetle. A great summary has been published by Michigan State University at https://www.canr.msu.edu/news/controlling_raspberry_cane_borer. Essentially, with the raspberry cane borer, it is necessary to remove the effected part of the plant by cutting off cane a few inches below the tunneled section of the plant. You will know you have successfully done this when your cut leaves healthy, intact cane. Timing is essential. Cutting of canes needs to be done prior to fall and winter die off of the cane. Also critical is complete removal of the infested sections of plant by burning or bagging for compost pickup. Also recommended is cutting back and removal of the stalks in the fall rather than letting them overwinter. Despite all of this, it will be necessary to keep a vigilant eye on the new growth next year to see if the beetle returns. If so, early detection and removal is important.
It's disheartening to experience such a pitiful harvest of raspberries this year, but it all serves as a good reminder and important learning that nature is variable, and ecosystems are far more complicated than what meets the eye at first glance. We got very complacent in expecting conditions to remain unchanged, and that just isn't how the natural world works. There are ebb and flow years, and with continual learning, we are able to manage conditions like the raspberry cane borer.