- To control the problem, you must first eliminate all visible signs of the fungus. Remove any leaves or flowers directly affected by sooty mold. Simply washing or wiping away the fungus will not remove the spores, so completely cut off the specific parts where mold appears. Wear rubber gloves to minimize your exposure to the fungus and use garden clippers or pruning shears.
- Pesticides will not kill a whitefly population in most cases, but the right pesticide can protect your gardenia. Spray your gardenia plant at weekly intervals with a neem oil pesticide. Neem is natural and not chemical-based, so it will not harm your gardenia, but it can help repel and even kill the whiteflies and other sucking insects that promote the growth of sooty mold. Spray the entire bush to contain the problem effectively.
- Sticky traps can reduce whitefly populations. Place yellow sticky traps around your gardenia plant to reduce the pest population naturally. When used in addition to pesticides, you can greatly reduce or even eliminate the pest problem. To make your own sticky traps, mount 1/4-inch plywood on thin wood stakes all around your gardenia bush. Paint the plywood yellow and coat it with an adhesive containing equal parts petroleum jelly and household detergent. You can also buy commercial traps at garden supply stores.
- Introduce a new insect into the environment. If you can verify for certain that the problem results from whiteflies, you can use one of the whitefly's natural enemies to help kill off the population. Ladybugs, commonly sold in garden supply stores, can help control whiteflies, as can lacewings and bigeyed bugs. If you are not sure whether you have whiteflies, note that they appear much as their name suggests. They are small, very lightly colored flies.