In Richard Moyer's recent note, he mentions cutting off floricanes before
fruiting. I assume he meant to say cutting off primocanes before fruiting. I
prune the tips of primocanes on primocane-fruiting black raspberries to
force multiple branching to increase the final berry count. However, there
is a catch. At some point in time, a node decides, somehow, to become a
fruit cluster instead of a potential new branch. If the primocane is pruned
above this node after this time, you reduce the fruit count instead of
increasing it, because there is only part of one fruiting branch instead of
having multiple fruiting branches. The descriptions I've seen of treating
primocane-fruiting blackberries mirror my experience on primocane-fruiting
black raspberries well enough that this caution may apply to blackberries as
well. You may not be able to arbitrarily keep cutting primocanes late into
the season.