Answer: Powdery mildew affects all cucurbits, but most often damages cantaloupes, squash, and pumpkins. Powdery mildew appears on leaves, petioles, and young stems as a white powdery mass composed of mycelium and countless numbers of spores. Under favorable environmental conditions the entire top surface of the leaf may be covered with the powdery fungus and an entire field may appear to turn white within a few days. Infections may also occur on lower leaf surfaces. Badly infected leaves become yellow, turn brown, and shrivel. The fungicide chlorothalonil (e.g. Daconil 2787), can be used on a preventative basis in home gardens. Sprays should begin at the first sign of disease and continue every 7-10 days thereafter. It may be too late this season to save your plants, but you can try. To prevent the problem next year, remove old plant debris from the garden this fall, choose varieties with resistance to the disease (several cultivars of pumpkin have moderate to excellent resistance to powdery mildew. Many cultivars of cucumbers and cantaloupes with excellent resistance to powdery mildew are also available.) and be sure to space your plants so they each have adequate sunshine and good air circulation. Any zucchini on your plant can be consumed without problem. At the very least wash the powdery mildew off the squash before cooking or eating raw. Best wishes with your garden!
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