June 20, 2008

Wet soils in alfalfa fields right after cutting are certain to do one thing — help weedy grasses like foxtail grow.

One option for managing these grasses is to let your alfalfa do the work. If you keep your alfalfa thick and thrifty, it will compete aggressively with invading foxtail. To do this you'll need thick initial stands and good soil fertility. In addition, harvest alfalfa only after it begins to bloom or when new shoots appear at the base of the plants so alfalfa can regrow rapidly and stay ahead of other grasses.

Unfortunately, this method may be easier said than done, and it sacrifices some forage quality since harvest occurs after bloom begins. So this method may not solve all your problems.

Herbicides are another option. Roundup® works great for Roundup Ready® varieties. In regular alfalfa, two chemicals that control annual grasses are Select Max and Poast Plus. These herbicides work well on seedling grasses that are less than 4 inches tall, and alfalfa tolerates both herbicides very well. Another herbicide option is Gramoxone Extra. Gramoxone burns back top growth of all green plant material. This will kill most annuals like foxtail, but it also can injure alfalfa regrowth that has already emerged. Only use Gramoxone immediately after harvest and before new regrowth shoots appear.

None of these herbicides have any soil residual activity, so good plant coverage is necessary and you may need to repeat the spraying if new weeds sprout.

If weedy grasses are a problem in your hay, thick and vigorous alfalfa stands and some well-chosen herbicides can help you get it under control.

Bruce Andreson
Extension Forage Specialist