Has any herbicide been sprayed nearby recently? That is one possible cause. Another is worse news -- it could be Rose Rosette Virus (RRV), which would be fatal for the rose. If the stems with these weird leaves look extra thorny and/or thick, that's another bad sign toward RRV -- but I can't see it in this pic. Google "Rose Rosette Virus" for images and compare it to your rose. Be aware that many roses have reddish new growth, so don't go by color alone. Look at the other characteristics. :-/ ~Christopher

If I grew iceberg in Virginia, it would lose all of its leaves also because of blackspot fungus (BS). Some roses are more susceptible to BS than others. If you want leaves on your iceberg, you can spray it with a fungicide (tebuconazole is a good choice). Or you might prefer to replace your iceberg with a different, more BS resistant rose.

midorit, ALL roses go through rest periods between what are known as "flushes" of bloom, and even though Knockouts are known for fairly continuous bloom, even they have down periods. And yours has been going through some trauma and stress. Don't overthink it, and don't kill it with love, lol. Keep it moist, not wet, and let it recuperate a while. Consider it normal for your rose to rest up to several weeks between flushes, depending on its health and the weather. When it finishes each flush, you can fertilize with a good rose fertilizer according to directions. Epsoma Rose-tone is good for long term health; a granular food is good for a quick boost. DON'T overuse the granular, it can burn the roots. But there are as many types of rose food as there are rose growers, lol. A time-release food works, too, and it's harder to overdo it. By the way, if that pot is sitting directly on the ground, it won't drain properly and you'll eventually cause the roots to rot. Raise it up on pot feet (or anything solid to get it off the ground) so the drain hole is unobstructed. Any Home Depot or Lowe's carries the nice terra cotta pot feet.

I do not know what it is but mine have it also. Horrible spring weather. Very little sun, too many drippy days and cold. I did receive downey mildew thru the mail this year. This was the first time I had ever seen it. The box and I ran for cover after opening. Here is the best that I can say. Downey mildew does not cross main veins. It will travel in-between them. Then something I never knew before was to turn the leaves over. Then look for the sparsa spores. If it is downey mildew it will be there. On the underside of the leaf below the downey patches there will be white patches of spores. They can be hard to see so I used a magnifying glass. They look like tiny little white dots in patches. Yes my new rose had downey mildew. My leaves that look like yours do not have the sparsa on the back. Now is the perfect weather for black spot and anthracnose and my roses are now getting both. I've been no spray for quite a few years now and only purchase the healthiest of roses. Will sad to say that does not mean that they won't get anthracnose. I did learn last year that if I did nothing it was very hard on the roses. Maybe since conditions stayed good for anthracnose nearly all of last year. In order to get things under control I have already sprayed this season with Bayer disease control (not 3 in one). Good luck in your quest to keep your roses healthy. I'll report back if I have any luck. I'm afraid if I delete this 2nd comment that both will disappear so I'll leave it.