Poor raspberry production
I have a 60’ long (3 plants wide) raspberry patch in Duluth, MN that has been successfully growing raspberries for the last 50 years until 3 years ago. The patch has been well weeded, de-canded, and fertilized every year. Not much different has taken place except that three or four years ago we side dressed the plants one fall with a local farmers manure. We also added a couple of blackberry plants to the end of the row. For the last 3 years, the raspberry crop has really dwindled and many of the berries are not fully formed. The plants themselves look vigorous and healthy. They do not appear to have any of the blights pictured on your website. The only thing that seems possible is poor pollination, however, our neighbor across the lake from where we live has had excellent success with his raspberries so poor pollination seems unlikely. What is your recommendation?
If you have been growing raspberries in the same location for 50 years, the plants have been productive far longer than is usually the case. This excerpt from a University of Wisconsin bulletin explains why:
The decline is usually caused by the growing presence of raspberry pests and diseases over time.
Go here to read the complete bulletin (especially note the section titled "Problem Solving):