I have a couple areas i had food plots in and have decided to take these and plant Cave & Rock switch grass in them. These plots last year had Paul cereal grain plots in them I sprayed the winter rye killed it and mowed it. Some of the clover is still in there in spots and a few weeds. The plan is to frost seed the cave & rock in there Late Feb then spray with Simazine early april Should I kill it with roundup now while what is still there is green? Any other advice?