Pine trees

[coon hunter]

I am building a house in a 12 acre pasture. I don't want a 12 acre yard so I'm going to plant some pine trees on one side. This pasture has been mowed well the last few months. I have all sorts of grasses, I mean all kinds. Fescue, signal grass, Texas panicum..... What should I be doing right now to prep for planting the pine trees in December-February. I am a farmer and I have ALL sorts of chemicals, but what should I spray now and what should I spray 6 months from now to control the grass in my pine trees. I can kill the grass now but should I add a residual?