I am always hesitant to recommend herbicide based fall weed control except in a couple situations. If the weeds are annuals frost will soon take care of your problem. If the weeds are perennials there's a very low chance you will get acceptable control as the growth cycle is nearing an end. Does 2,4-db have a residual? Probably but it won't affect grasses. It is a broadleaf herbicide. If the wheat is the question, well, you know the rest of the statement. Ah, to complete the thought for others, wheat is a grass. Or, maybe, I missed the point?