Hi Brian,
Crossbow...if I got the name right....was a new product that the guy at the extension office was giving to interested farmers to control their multiflora rose in fields/fences. It was said to be systemic, as is RoundUp, but had a better absorption rate through the woody tissue. It may be called by another name now....with everything else we needed to do, multiflora rose didn't seem to be a big enough problem to really worry about...so there it sat.
BUT....you're right, if I'm going to use anything on these cuts....it would probably have to be during it's growth period to be effective.
Che