Powdery Mildew on Knockout Roses
I have a lot of knockout roses that I have had a couple of years and have had no problems, but this spring on mostly my rainbow knockouts and some of my double bloom reds and pinks, they have on them something that looks like powdery mildew. It hasn't affected the doubles as much as it has the rainbows, as the rainbows look sick. I have tried spraying and cutting them, but it doesn't appear to be helping. What should I do?
Certified GKH Gardening Expert
Try neem oil. Very effective and not harmful to people or animals. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm