April 11, 2008 

Early weeds like downy brome, cheatgrass, and wild oats can be a big problem in pastures. They reduce pasture quality and carrying capacity.

Warm-Season Pastures

In pastures dominated by warm-season grasses, one control option is to spray one pint of glyphosate, like Roundup, per acre as soon as weedy bromes start to green up but before warm-season grasses start growing. This should solve the problem for this year and knock out other early weeds like bluegrass without harming warm-season grasses.

Another option is to use 4 to 6 ounces of Plateau herbicide, which will also provide some residual herbicide activity for later emerging weeds as well.

Cool-Season Pastures

Weed control in cool-season grass pastures is tougher. Both glyphosate and Plateau harm cool-season grasses. Gramoxone is a better choice, but don't spray until the weedy bromes are about to form seed heads. Gramoxone will kill all the green top growth it contacts, including weedy bromes. This will eliminate them producing seed this year and your intended grass will start to regrow in two to three weeks.

The seed of these grasses can last several years in the soil, which means you should plan to repeat sprayings for several years. Once you've gotten rid of the weeds, be sure to graze the pasture to maintain the vigor and competitiveness of the desired grasses.

Bruce Anderson
Extension Forage Specialist