Two trees on my property have a chronic habit of putting up what I believe are called water shoots, or water sprouts - branches that sprout straight upward from main branches. I diligently prune them out as often as I can, as they look bad and I believe they don't do what the rest of the tree is supposed to do - bear fruit in the case of the old apple tree, or bloom in the case of the ornamental cherry that is my street tree. But every year they seem to recur. It's a tiring task, and I'd prevent their growth if I could. What are they a response to - is it lack of water?