A nub, or dog's ear, is the piece of a twig or branch that is left behind after a bad pruning job.
Leaving a nub sticking out interferes with a plant's natural ability to heal a wound. It also creates a foundation that can catch leaves, providing the perfect shelter for problem bugs and fungi. The nubs themselves, being too far from the branch collar for proper healing, often take longer to heal or don't heal at all. This provides an easy entrance for fungi and borers.
To properly prune a twig or small branch, it is best to cut as close to the branch collar as you can. The branch collar is the ring from which a twig emerges. Do not cut the branch collar. There is no need to paint or treat a properly trimmed branch. Plants already know how to handle that on their own.
So, off with their nubs!
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.