See:
Raspberry (Rubus spp.) - Cane Blight
Note: 'Boysenberry', 'Loganberry', and 'Youngberry' canes are seldom infected with cane blight unless canes first are frozen, pruned, or mechanically damaged. This pathogen is a wound invader and is rarely is a problem in hand-harvested fields. On trailing berries, blighted canes turn gray and often show black specks containing the fungal fruiting bodies (pycnidia). Remove infected canes, prune near the ground, switch to drip/trickle irrigation, and/or use the alternate-year fruiting system. Direct chemical sprays to the cane's base during or immediately after harvest or after pruning.