Answer: Begonia leaves can be attacked by powdery mildew, a fungal disease. The plants are prone to the problem, but you can help them avoid it by providing lots of air circulation around the plants. The disease often takes hold when environmental conditions are right (warm days, cool nights, some humidity) and air circulation is poor. Remove the affected leaves to stop the spread of disease. 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.
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