What actually broke, the laterals from the main canes, or the little fruiting branches from the laterals? Laterals would normally be tied onto the trellis and not break. Some blackberry varieties have fragile stem nodes, Obsidian is one.

I just doubt that irrigation would be a factor in fragility.

I just tied the main cane and the main laterals to the trellis wire not the fruiting lateral, there seems to many to actually do this, I'll try it next year and maybe cut any that I can't support. Maybe I just have to many laterals and am not training them correctly. I'm going to try to find a pick a patch and see how they do it. The berries are huge on the PAF and makes since they might need help with support.

The fruiting spurs just tend to lower gradually with the increased weight of fruit, should not break. I assume squirrels are running through the varieties equally, that is not desirable and I would set traps.