I have a flower bed with dahlias that I planted a few months ago and now these white powder-like things are appearing on the leaves and flowers. I've already tried soapy water but it's not helping much. What can I do to save the plants?
Have you checked the undersides of the leaves to see if there are little bugs there? It could be powdery mildew (a fungus) or mealybugs, and if it's powdery mildew, you're gonna need a fungicide - soap alone won't cut it. Try a fungicide specifically for powdery mildew at garden centers, or even sulfur powder works pretty well. If it's actually a pest (those little white bugs), then you can use an insecticide or neem oil, but make sure you apply it to the undersides of the leaves too since that's where they like to hang out.
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