Source: University of Nebraska Extension
Early spring weeds such as cheatgrass, wild oats, and downy brome often are a problem in native grasses, but you can limit their damage through grazing or herbicides.
The seed of these grasses lasts about three years in the soil, meaning they can be a problem for several years.
In grasslands dominated by warm-season grasses, one option is to spray 1 pint per acre of glyphosate early this spring after the weedy bromes green up but before warm-season grasses start growing. This should provide control this year and knock out other early weeds like bluegrass without harming your warm-season grasses.
Another option is to use 4 to 6 ounces of Plateau herbicide or its generic equivalent to achieve similar control. With Plateau, residual herbicide activity also will control some later emerging weeds.
If you'd prefer not to use herbicides, you'll need to limit seed production with grazing. Begin grazing as soon as these bromes green up this spring. Using these pastures for calving might be a good option. Graze the pasture hard to keep seed heads from developing.
Eventually these grasses will form heads just an inch or two above the soil surface and grazing will no longer help.
Remove your animals from this area for six weeks or longer to let the desired grass grow and regain some vigor, feeding hay, if necessary, during this period. Repeat this hard early grazing for a couple springs and you should start seeing results.