There are several natural fungicides that can be used to treat strawberry leaf diseases. One of the most effective is neem oil, which is derived from the neem tree and has antifungal properties. Other natural fungicides include baking soda, which can be mixed with water and sprayed on the leaves, and garlic, which can be boiled in water and used as a spray. It is important to note that while natural fungicides can be effective, they may not be as potent as synthetic fungicides and may need to be applied more frequently.