Answer: Roses need lots of sunshine and good air circulation all around to help them avoid powdery mildew. While some plants are more prone to it than others, improving the sunlight exposure and air circulation will certainly help. Once you notice the powdery mildew, the plant is already infected so you may have to resort to sprays. to control this disease, you must treat over a 10 day to two week period. Sodium bicarbonate commonly known as baking soda has been found to posses fungicidal properties. It is recommended for plants that already have powdery mildew to hose down all the infected leaves prior to treatment. This helps to dislodge as many of the spores as possible to help you get better results. Use as a prevention or as treatment at first signs of any of the diseases. To make: Mix 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil (canola oil, soybean oil, olive oil, or neem seed oil) with one gallon of water. Shake this up very thoroughly. To this mix add 1/2 teaspoon of pure castille soap and spray on your plants. Be sure to agitate your sprayer while you work to keep the ingredients from separating. Cover upper and lower leaf surfaces and spray some on the soil. Repeat every 5-7 days as needed.
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