Powdery mildew, of the scientific name Oidium, can grow on just about anything if the environment is right. Many garden plants and fruit trees are susceptible to powdery mildew, which creates a cosmetic problem and can destroy flowers and crops. Treat powdery mildew using methods that will kill the fungus and make the area in which it was growing inhospitable to further fungal infection.
Remove all infected parts of the plant. If your plant has fruit or flowers covered with this sooty, powdery, black, white or gray substance, then remove the fruit or flower and check the stem, which probably also needs to be removed. Clip branches and twigs using sterile pruning technique, which requires you to rub down your clippers or shears with rubbing alcohol after each cut.
Dispose of all infected debris. Place it in the garbage bag and remove the debris from the area. If you leave the cuttings on the ground, the powdery mildew will not die but will just keep growing and spreading.
Treat the plants with a powdery-mildew specific fungicide. If the plants are fruits or vegetables, the fungicide should be safe for human consumption.
Water from below. Use a drip hose to water your plants rather than a sprinkler system. Sprinklers soak the leaves of the plant, making a moist environment for the powdery mildew to grow in.
Keep susceptible plants in full sun. This will help keep leaves and branches dry so that the powdery mildew cannot return.