Provide your fence with plenty of sunlight. If parts of your fence are constantly shaded by trashcans, shrubbery, yard tools, wood piles or other objects, move these objects out of the way to ensure that your fence receives ample sunlight. Mold spores cannot breed in the path of direct sunlight.
Place a mixture of 3 qt. water, 1 qt. household bleach and 1/4 cup of ammonia-free dish washing detergent in a spray canister (like those used for insecticides, available at hardware stores) and spray the entire surface of your fence. Wait about 15 minutes and rinse with a standard garden hose. The Journal of Coatings Technology recommends this approach for killing trace mold spores and preventing mold growth on all types of wood fences, as the bleach acts as a repellent for mold. Perform this operation sparingly, no more than once a year, as excess bleach exposure may lead to discoloration.
Paint your fence with a fungicidal sealant. This is especially important if you live in a humid or moist environment where your fence receives extensive, prolonged exposure to damp conditions, a prime breeding ground for mold.
Examine your fence regularly for signs of mold contamination, which resembles a black, gray, brown or sometimes white discoloration, usually powdery or paste-like, and sometimes accompanied by a musty odor. If you notice the presence of mold, remove it immediately to prevent the spores from spreading. Use a standard spray bottle to spray the area with household bleach or lemon juice, both of which destroy mold on contact. Wipe the area with a cloth or rag to remove the spores.