Oil & Dish Soap for Mold on Plants

A Moldy Mess

• The term sooty mold applies to many types of molds that grow on plant surfaces, including leaves and fruit. The blackish substance can be rubbed off with your fingers, and while not usually that harmful, if it gets thick enough, it can affect a plant’s ability to photosynthesize. Other mold-like substances, such as powdery mildew, can be treated similarly despite the fact that they are not technically molds.

Go to the Source

• The direct cause of the mold is the secretions of insects like aphids, scales and whiteflies who feed on the plant, then deposit their honeydew on its surface, encouraging the growth of mold. When treating mold with oil and soap, you are actually targeting the insects who led to its growth. Therefore you must ensure thoroughly coated leaf and fruit surfaces when spraying because you don’t want to leave any remaining surface area for insects to colonize. Spray both sides of leaves with the soap-oil solution until it drips off. Note that molds not caused by insect honeydew, such as botrytis or gray mold, are unlikely to be affected by applications of oil and soap.

Recipes

• Several combinations of soap and oil are effective. Try 2 tablespoons of cooking oil and 2 tablespoons of baby shampoo in a gallon of water, adding 2 tablespoons of baking soda if the mold is already present. Shake well and apply every five to seven days. Or make a concentrate of 1 tablespoon mild dishwashing detergent with 1 cup vegetable oil and mix well. Then combine 1 to 2 teaspoons of this concentrate with a cup of water and spray once a week for two to three weeks.

Safe Use

• Although home ingredients like oil and soap don’t pose a hazard to humans or pets, they could be dangerous to your plants if you don’t apply them correctly. Never spray substances like soap and oil in sun. Instead, wait until evening so the sun’s rays don’t burn the leaves. Water the plant the day before to ensure its robustness before receiving the treatment, and avoid using on plants with hairy or fuzzy rather than waxy leaves.