Weathering releases zinc and copper that kills any remaining moss and prevents further moss growth. Copper wire strung every 10 feet horizontally along the butt ends of shingles provides some control. Zinc and copper flashing are available at most hardware stores. Metal ridge tops can be purchased through roofing companies or your local building supply store. The two most common active ingredients in these materials are copper and zinc.
Control is best when the moss is actively growing.
In most cases, apply chemicals when rain is not expected for a few days. Moss controlling chemicals come in liquid, granular or dust formulations. Applying liquids with a hand-held sprinkler can help reduce drift. Don't spray on windy days if you use a hose or mechanical sprayer. Some powder products are applied to the roof dry and require moisture to spread them.