Cane borers in my mid-Michigan raspberries
Only after my raspberries were decimated this year did I get online to try to figure out what happened. Based on what I've read here, I am guessing these beetles will be back next year. I read they lay their eggs in soil. I have trimmed back everything (6-8" of cane left) and burnt the bushes. I am also thinning out the plants more aggressively than I have done in the past. Is there anything else I can do this fall?
Next spring I will be looking for wilting tips and hopefully get them before they've ruined my berries!
May I ask one more question: the berries have not been as sweet in the past few years as when they were first planted. Perhaps thinning more will help. Should I be amending my soil, perhaps? Thank you so much for your advice.
Gratiot County Michigan
I am not quite sure what pest you are describing. There are two common raspberry cane borers in Michigan, the raspberry cane borer and the rednecked cane borer, neither of which lay their eggs in the soil but in the raspberry canes. I have never seen the rednecked borer but the raspberry cane borer is pretty common.Controlling the is pretty simple. The wilting shoot tips you describe are the result of girdling the stem after the female lays an egg in the stem. You need to remove the girdled section when you see the wilting and hopefully you will remove the egg as well. If there is a hole in the stem this indicates the the larvae has hatched and is burrowing down into the cane. Remove the cane down past the larvae. Since you removed the canes down to 6 inches already examine those canes to see if there are holes in them. It sounds like you have already removed the larvae so next year you need to worry about beetles moving into you patch to remove wilting stems as you see them. Here is a link to an article, with pictures) I wrote several years ago on controlling this pest.
Thinning the canes in the winter to about one cane every 8 to 12 inches and heading the remaining canes to about 28 inches will force the plants energies into producing larger and sweeter fruit.
You will also need to control the spotted wing drosophila a new invasive pest of raspberries and other berries. This pest has really destroyed the fall raspberry industry in Michigan. Commercial growers are forced to spray their crops at least once a week to protect their crop. Picking the fruit every day or two will reduce the amounts of fly larvae in the fruit. Once the fly moves in it will quickly destroy all the berries.
Here is a link to the Spotted wing drosophila web page.