Powdery mildew on zucchini plants

You could spray the copper spray on the existing soil to kill any over wintering spores but the truth of the matter is that the spores are already blowing about anyway. First, make sure to prepare the soil well so that it will hold adequate moisture between watering. Stressed plants are more susceptible to disease. We like Loam Builder for the ground and Organic Potting soil for containers. The addition of Agricultural Lime will provide necessary calcium which not only inhibits blossom end rot, but also helps with disease resistance. Choose varieties that are hardy such as Burpee Hybrid or Black Beauty. Avoid getting the leaves wet and water only in the mornings. It is normal for zucchini to have silvery white patterns on the leaves. Don't confuse them with powdery mildew. There has been recent research that shows zucchini were protected from powdery mildew by spraying them with a water/milk solution. That's right, milk. Spray the plants in the morning every other week with a solution 1 part milk to 9 parts water. Resist the temptation to increase the milk. Not only did this spray act like a foliar food, but infections were controlled by the spores contact with calcium in the milk.

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