Triple crown blackberry leaves drying up?

I've got some primocanes that have their leaves drying up and eventually falling off. The top leaves are perfectly fine but I notice the ones closer to the soil are looking like the image. Been cutting the bad leaves off, but worried if it is fungal or what.

I cut back my floricanes already, the primocanes have already been topped and ready for next year haha. Just don't want the primocane leaves to all drop