I planted a blackberry bush (actually, several) last year. This year, one of them sprouted HUGE middle canes (are they called canes?). They must be 8-9 feet tall. They're thick and really freaky looking, and yes, they are part of the blackberry bush. Also, I have a good number of berries on this bush---I would have thought a lot of energy is being expended on growing those huge middle canes. (Or whatever theyre called.)

Don't know the name of it, but I bought it at Lowe's. Nothing fancy. Came in a little bucket.

Should I prune them? Trellis them? I've googled for hours, and cannot find an answer to this question. Thanks in advance!