What’s a good chemical to use around the farm yard that will control and kill the weeds and grass.

Pramitol. Ground sterilizer. Suppose to hold for one year

I've heard of guys mixing Roundup and Liberty. Never tried it myself but they say it's dynamite.

Round up, unless you have ridden that horse into the ground and beat it dead. A little 2-4d with the round up will kill about anything, but won't keep weeds from germinating another flush. From what I have observed round up at the rates used in hand sprayers around the yard(soak it until it runs off)will even kill round up ready crops.