High humidity and mild temperatures can bring on mildew especially with new foliage in the spring. Overhead watering, shade and poor air circulation will make matters worse. It’s best not to over-fertilize ninebarks, limit the plants around the base and mulch the dirt. Usually, a little bit of mildew is not a problem. And, making a few changes listed above will help. However, if you are concerned that the mildew is really affecting the health of your plant, your garden center can help you with a fungicide.
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