Summer annual grasses are rarely a problem in western Washington, or in the Willamette Valley and coastal areas of Oregon. They may be a problem in areas east of the Cascades throughout the Northwest and south of the Willamette Valley in Oregon, depending on local conditions. In controlling annual grasses, it is important to positively identify the grass before acting, to avoid wasting time and chemicals treating perennial grasses.
Preemergence herbicides are very effective in controlling grasses such as crabgrass, barnyardgrass, and foxtails, if applied before they germinate. If annual grasses are consistent problems, apply chemicals in spring when soil reaches 50 to 55°F, the temperature needed for germination. In some areas, this may coincide with late forsythia bloom. Irrigate after application of all preemergence herbicides to incorporate them into the soil where seed germination occurs. Once weedy grasses are observed, it is too late for preemergence control.
Annual grasses are generally difficult to control once they have infested turf. Selective postemergence control is best accomplished if annual grass seedlings are treated when they are small (i.e., five-leaf stage or younger).