Epicormic Growth

This growth occurs on the trunk and at the bases of branches. It is straight in nature and grows very quickly; this  is because it is diverting energy from the canopy.   This diversion of energy from the canopy is very detrimental to it and will weaken it, even leading to dieback.  

If it is never allowed to see a Sunday and is removed frequently the energy can be retained within the canopy.

When pruning, leave a collar on the cut, do not pare it back to the bark. This leaves a smaller surface area for the tree to repair.