Answer: Sounds like your rose bush has powdery mildew. It's difficult to control once it has a foothold, but you can cut out the infected plant parts and be sure to clean up any fallen leaves and blossoms so the disease won't spread. Next spring avoid the disease by making sure the rose bush gets plenty of sunshine (at least 8 hours) and has enough space around it for good air circulation. There are a few fungicides on the market that you can use to stop powdery mildew if it becomes a problem again next year. The safest is one called 'Rose Defence'. It'sa neem oil based product, biodegradable and is safe for insects, animals and humans.
The insects might be aphids, thrips, or whiteflies - all are common on rose bushes. Capture a few so you can have them identified at your local nursery. Once you know what you're dealing with, you can find an appropriate spray.
Best wishes with your roses!
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