In RCCA/AMA rules combat, we put some sticky substance on the wings to snap and rip the streamers. Prop cuts also occur. And sometimes you get a cut with the tail and I've even seen two streamers get knotted and one get pulled off. So basically "any way you can". In RCCA/AMA rules, the only thing that isn't allowed is devices built on to a plane just to cut a streamer, so you can't have some bits of rod or whatever hanging off to try to cut streamers. In some areas guys fly combat with their own local rules that sometimes don't allow wing stickum and such. In that case, it pretty much comes down to prop cuts.