There are many different types of diseases that can infect your tree. Some of these diseases are caused by a fungus. North Dakota State University lists Verticillium alboatrum and sooty mold fungi as two types of fungus that commonly infect trees. If you find that your trees are infected with a fungus, you will need to treat them before the fungus has a chance to spread.
Purchase a fungicide with the active ingredient captan. This fungicide is used to treat a variety of fungal diseases in trees and shrubs.
Take proper safety precautions. You will need to wear a long-sleeved shirt, long pants, shoes and socks, waterproof gloves and goggles. Fungicides are harsh chemicals that can cause skin irritations, damage to the eye and allergic reactions.
Mix 4 lbs. of captan fungicide with 20 gallons of water. If your spray tank doesn't hold 20 gallons of water, you can mix 2 lbs. of fungicide with 10 gallons of water, or 1 lb. of fungicide with 5 gallons of water.
Spray the fungicide directly on your tree's leaves and trunk. Cover every area where you see the fungus.
Repeat every two weeks until the fungus has cleared up.