UNL CropWatch July 23, 2010: Controlling Summer Weeds in Alfalfa

UNL CropWatch July 23, 2010: Controlling Summer Weeds in Alfalfa

July 22, 2010

Wet soils in alfalfa fields right after cutting can encourage weeds and grasses to get a foothold, but with good management you can help give your alfalfa a competitive edge.

The best way to start is to keep alfalfa thick and thrifty so it will compete aggressively with invading weeds. Maintain thick initial stands, good soil fertility, and harvest alfalfa only after it begins to bloom or when new shoots appear at the base of plants. With this head start, alfalfa should regrow rapidly and out compete young weeds. Unfortunately, this method is easier said than done, and forage quality will be lower if harvest occurs after bloom begins.

Herbicides are another option. Roundup® works great for Roundup Ready® varieties. In regular alfalfa, Select Max® and Poast Plus® can be used to control annual grasses. These herbicides work well on seedling grasses that are less than 4 inches tall, and alfalfa tolerates both herbicides well. Neither of these herbicides has any soil residual activity, so good plant coverage is necessary and you may need to repeat the spraying if new grasses emerge.

For broadleaf weeds, consider Raptor® and Pursuit®. They also need to be applied before weeds are 4 inches tall. Both products have some residual activity so you can apply them a little early and still get control of many later emerging weeds. They will, however, also set back your alfalfa a little.

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

Note: Read herbicides labels carefully and follow all label directions.

Bruce Anderson
Extension Forage Specialist


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