This is damage from the severe winter we had. I could be wrong, the picture's not that clear, but is that new growth I see appearing on the left, below the damaged area of trunk in the picture? If it is, leave that alone - suggest you wait and see what happens, but if that area of bark gets worse or spreads more, cut the whole thing down to where that new growth is, and let that take over. If there's new growth at the base, even better, you can cut it down to there if you prefer.