Wind? Accidental foot traffic? Those new basals are so dang tender. Maybe critters rustling through your roses?
A rabbit would've eaten it...
Susan

Squirrels have done this in my yard. Rabbits or deer too, or a stray cat or dog.

Hmm, I think the picture doesn't really show the damage well enough. It wasn't broken or bent, something ate the center out of the cane. I cut the shoot off with my pruners because I was worried whatever ate out the pith might still be in there working it's way further down, but after cutting it off I didn't see anything. I think it must be some kind of boring insect, but I've never seen 'rose borer' damage before so I came here for independent verification.

Deer and rabbits have never been a problem in our particular area, too many dogs for them to feel comfortable I think.

This post was edited by peachymomo on Wed, May 21, 14 at 9:50

That is freaky. I have bad borers, but they bore into harder canes, when they are more like wood. Mine go bonkers and bore for feet :(

Spinosad may be worth a shot, but I don't know what kind of borer that is. Definitely cut out and dispose of any canes like that, and I'd try several rounds of spinosad (just a guess at what might help, keep in mind). Make sure to spray it late in the day when the bees are in for the night, though. It's toxic to them until it dries.

I hope someone can ID what exactly is going on, though!

This kind of damage is not caused by the little bees and wasps that drill the cut cane ends. It is a beetle larva or sawfly larva. Check out "raspberry horntail," a western sawfly.