Not sure exactly what the circumstances are since there are no photos but if the branches/tissue are already dead there is no reason or benefit of applying anything. I would recommend you cut the dead part of the branch back to the next branch coming off of it to help clean it up appearance wise. If its really hot out you could also slather some Vaseline on the cut to help keep the moisture in and prevent the branch from transpiring around the cut causing die back to occur from the cut down the branch.