You will want to band your trees in the fall. When the weather starts to get cooler, the adult canker worms hatch. After breeding, the wingless-females crawl up the tree to lay their eggs. You need to catch them before they reach the highest point of the tree, where they want to lay their eggs.
If you can band your trees before they hatch, you can catch them before they lay their eggs. This will prevent the inchworms from getting in your hair- and defoliating your trees- in the springtime, when they hatch.