PRUNING YOUR SHADE TREES : Page 77
Where a young tree has a main fork low in its stem, steel yourself to amputate one leader or the other so that the survivor can take command. A close look at how the competing leaders grow will tell you which to condemn.
Direct your attention next to sucker growths. These are straight, unbranching shoots that you don't want to become important members. They only consume energy and clutter form. They may come up from the tree's roots or
out of its trunk or off main members. Prune suckers ruthlessly, using your shears and pole tools. There will be more suckers next year in case you need any to fill out a pattern.