Answer: Ninebark is occasionally subject to mildew problems when weather conditions are just right. It is a fungal infection. It will not kill the plant although it can look a bit ugly. If it is just starting to appear it can sometimes be controlled by immediately removing the affected foliage and cleaning up any fallen foliage and disposing of it in the trash. If it is fairly widespread, it is far more difficult to control. In general, it helps to have the plants growing in a location with good air circulation, thin them so air can circulate inside the plant, and avoid watering them in the evening. In the fall, do a thorough clean up around the plant to limit sources of reinfection. Hopefully it will not reoccur next year.
Give your Royal Robe lots of sunshine and adequate water and it should grow vigorously for you. It's an easy care plant and should bloom all summer for you. Enjoy!
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