Answer: What you describe sounds like powdery mildew, a fungal disease. I don't think it has anything to do with the mulch you applied to your garden. It is a fungus and it is airborne. There are several effective fungicides available for different sites and plants, but use on plants varies with each product, and not all fungicides registered for use to treat powdery mildew may be used on all plants. Be certain the product you purchase is labeled for the intended use(s), and follow directions on that label. Some products with a broad range of applications for outdoor ornamentals include products containing: Bacillus subtilis, neem oil, potassium bicarbonate, sulfur or lime sulfur.
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