Many weeds can be controlled while establishing a switchgrass stand.  Some can be controlled with fire in late winter by burning off residue and stubble.  Other weeds are essentially controlled by vigorous switchgrass growth.  The lower three images show an old thin switchgrass field that has weeds, but by mid June the switchgrass has outgrown all but the tallest weeds.  In more vigorous fields weeds should be smothered out several weeks earlier.