Close to the base of the target tree, point the hammer down in a copper nail at a slight angle. There is no standard, as far as size when selecting copper nails, but usually the more surface of the nail in terms of length and width, the more effective the treatment. Even a longer nail means deeper penetration, which leads to a higher chance of the tree that becomes sick. Place nails in a ring around the tree, about half an inch apart. This damages an increased number of growth cells and increases the concentration of copper in the tree. This higher concentration is better because it increases the chance of metal oxidation that poisons the tree. The idea that a copper nail will kill a tree only applies to very small trees such as seedlings.
eBay