No plug will fix that kind of flat because its glass (more of a linear gash) instead of a nail (puncture). Also because its in the middle where it realy heats the hell up a plug wont do the trick. I suggest getting a new tire. There is another option that you can do. You can take the tire off and patch it from the inside but I dont know how well that will work considering the puncture is in the middle and I dont wannna be responsible for you wrecking from the patch not holding. So yea on the safe side get that new tire on there.