Winter Annual Weed Control with Herbicides in Alfalfa-Orchardgrass Mixtures

Abstract

Alfalfa–orchardgrass hay is popular in the Western United States because of an expanding horse-hay market. However, weed control in mixed alfalfa–orchardgrass stands is problematic, as herbicides must be safe for both species. Most growers rely solely on the competitiveness of the crop for weed control, which is often insufficient, especially in older stands. Field experiments were established in northern California to determine the efficacy and crop safety of several herbicides for winter annual weed control in established alfalfa–orchardgrass. Metribuzin at 560 or 840 g/ha and hexazinone at 420 g/ha applied in late fall provided at least 95% control of shepherd's purse and at least 80% control of downy brome without crop injury. Imazethapyr at 70 g/ha applied shortly after crop green-up provided more than 85% control of emerged mustards without crop injury. Paraquat at 560 g/ha applied shortly after crop green-up gave 50 to 82% weed control and caused significant injury to orchardgrass, which was still ...