I have three recipes that may work for you, courtesy of 'Jerry Baker's Backyard Problem Solver'. (-a wonderful gardening book that ANY gardener should not be without) The first tonic is for black spotting, hence it is called 'BLACK SPOT REMOVER TONIC': 15 tomato leaves, 2 small onions, 1/4 cup rubbing alcohol; chop tomato leaves and onions into finely minced pieces, and steep them in the alcohol overnight. Use a small, sponge-type paintbrush to apply the brew to both tops and bottoms of infected leaves.
next we have a recipe called 'FUNGUS FIGHTER TONIC'-1/2 cup molasses, 1/2 cup powdered milk, 1 tsp. of baking soda, 1 gal. of warm water. Mix the molasses, powdered milk, and baking soda into a paste. Put the mixture into the toe of an old nylon stocking, and let it steep in a gallon of warm water for several hours. Then strain, and use as a fungus fighting spray.
*Last but not least: the POWDERY MILDEW CONTROL TONIC- 4 tbsp baking soda, 2 tbsp Murphy's Oil Soap, 1 gal. warm water. Mix all ingredients together. Pour into handheld mist sprayer, and apply liberally when you see the telltale white spots on your plants, or even before.
Good Luck
Tempest~