I found these odd shells on a stem of my rose bush and have looked around online and can't find out what they are. I don't think it's scale because the pattern is so uniform - they are hard shells and underneath it looks like they have cut a single slit in the stem.
Any ideas what this is?? It looks intriguing, but I'm also wondering if it's a pest or disease, and therefore snip this stem off the bush. Thanks for your help!