I used to wonder why I never got ahead of the raspberry/blackberry cane
borers. Every Fall, when I cut out the dead canes, I religiously
scrutinized primocanes for swellings on stems, cutting out and destroying
infected canes. I do it again in late Spring/early Summer when cane borers
are actively infecting new, growing, canes. Every year there seems to be as
many (or more) than the year before but I think I just figured out why.
I had always centered my attention on the obvious swellings that
circumvent canes. These swellings are almost all located at the bottom 1/3
of the canes. This year, looking higher, I'm seeing a different pattern.
Cane borers are infecting the upper portions of primocanes with a different
type of girdling. Instead of the grub circumventing the cane and ending
where it began, the upper cane borings are girdlings in spiral patterns.
These girdlings span 1-1/2, or more, of the cane's circumference. The worst
part of it is that they are somewhat difficult to see because they are not
as pronounced and lower cane borer swellings tend to be. I observed some
swellings only after the light struck them at a favorable angle.
If we do not cut out these infected canes, they (the canes) will die
just before the fruit ripens and that is FRUSTRATING. Even if there was a
spray recommended for controlling them, we couldn't use it anyway because
many infections occur during pollination. Sanitation is still the
recommended method of control and the best time to do it is now, while
primocanes are dormant.
Jim Fruth
Brambleberry Farm
Pequot Lakes, MN 56472
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