After my blackberry bush began to yield fruits, they shriveled and died. Also, why are my blueberries shrivelling and dying?
Blackberries Shrivel and Die
i don't know your area, but i'm from western PA and i know that too much water, too little water, too much sun and or heat are huge culprits. They tend to grow well along woods where they have sheltered sunlight, but not too hot. Do you have different berries (rasberries in particular) or a black walnut tree close? These things don't mix real well with blackberries. This has been my experience and i've grown berries my whole life. Also pruning them down will be a benefit. I hope this helps