March 19, 2010

Given the plentiful soil moisture conditions across much of the state, early winter annuals like cheatgrass, downy brome, and wild oats are likely to be a big problem in pastures this spring. Winter annual bromes can reduce pasture quality and carrying capacity.

Seed from these grasses lasts several years in the soil, which means you need to plan to repeat any herbicide spraying for several years to establish control.

In pastures dominated by warm-season grasses, one option is to spray 1 pint per acre of glyphosate, like Roundup, early this spring after the weedy bromes 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 or a generic that provides similar results. With Plateau, residual herbicide activity also will control some later emerging weeds.

If your pasture is cool-season grass, the job 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, even your good grass. After treatment, your good perennial grasses will start to regrow after a couple of weeks while the weedy grasses will be killed, eliminating their seed production this year.

Once you’ve killed these weeds, graze the pasture to maintain the vigor and competitiveness of the desired grasses.

If used correctly over several years, herbicides and grazing can help you manage these winter annuals to avoid yield losses in your pastures.

Bruce Anderson
Extension Forage Specialist