Oregon

In new alfalfa plantings, volunteer grain is a spring or late-summer problem while nightshade can hit in mid- to late summer, says Mylen Bohle, extension agronomist, Oregon State University. Apply glyphosate before planting or a grass or broadleaf herbicide during establishment. Volunteer grain can decrease alfalfa quality and yield, although it may increase total first-cutting yield if it doesn't reduce the stand. Nightshade toxicity could totally devalue a field.

In established alfalfa, bluegrass, quackgrass and dandelion are pests throughout the growing season. Apply herbicide (Velpar + Gramoxone) in fall. Depending upon stand, price of hay, etc., Kerb can be applied for grass control. The grasses dramatically reduce quality and stand life; dandelion reduces yield but not lab quality for the most part.

Midwest

Indiana

Foxtail grass species and several broadleaves — jimsonweed, cocklebur, pigweed and black nightshade — affect seedling alfalfa stands in first cuttings, says Keith Johnson, forage specialist, Purdue University.

Control options include: 1) seeding pure alfalfa for more herbicide choices, 2) scouting for all these weeds' presence as alfalfa and weed seeds germinate and become seedlings, 3) treating when weeds' growth can be stopped or 4) using companion crops like spring oats.

Foxtail reduces alfalfa composition and quality. With the broadleaf weeds, if not controlled, there's concern as to whether crops should be harvested because of possible toxicity. Thankfully, are all annuals.

Control curly dock in other crops rotated with alfalfa. In Roundup Ready alfalfa, glyphosate can reduce this weed's first-cutting impact. Curly dock's high-moisture, thick stems can mold within bales. Unfortunately, its seed can live in soil for many years.

Cressleaf groundsel has increased in Indiana as more row-crop fields are no-tilled. This winter-annual broadleaf can flourish in this environment.

Missouri

Summer annuals such as crabgrass, foxtail and pigweed affect spring-seeded alfalfa, and winter annuals such as chickweed, downy brome (cheatgrass) and henbit hurt fall-seeded alfalfa. Some herbicides control these species, but yields will be lower once weeds are eliminated, says Kevin Bradley, plant scientist, University of Missouri.

Curly dock affects established alfalfa throughout the season but mostly at first cutting. Few herbicides control it, but spot spraying with glyphosate where feasible is effective. No current herbicides will remove established curly dock from an alfalfa stand, he believes. Roundup Ready alfalfa would help if it were available, Bradley says.

Nebraska

Perennial bluegrass is a year-round pest in irrigated alfalfa, lowering quality and reducing stands, says Bruce Anderson, University of Nebraska forage specialist. To control it, manage irrigation well and spray.

Tall waterhemp, a late-summer competitor reducing quality and stands, can be controlled with vigorous alfalfa stands and herbicide application.

Winter-annual mustards decrease quality and yield of first-cut alfalfa and can be controlled if herbicides are timed properly.

Ohio

Winter-annual broadleaf weeds, especially wild turnip and wild radish, are difficult to control in fall-established alfalfa. So say Mark Sulc and Mark Loux, Ohio State University crop scientist and weed specialist, respectively, and Ron Hammond, entomologist at the Ohio Research and Development Center. They suggest applying broadleaf herbicide (for example, Pursuit) in fall for best control. The weeds slow drying time, reduce stand density and yield and usually lower forage quality.

Annual broadleaf and grass weeds compete with spring-seeded alfalfa, but postemergent herbicides, applied when weeds are small, can control most of them. If not controlled, they can harm stand establishment, yield and forage quality.

Perennial weeds, mostly dandelion, curly dock and Canada thistle, are problems in older stands, primarily in spring. Control before seeding alfalfa; then maintain thick, vigorous stands with good fertility and proper harvest schedules. Herbicide control is problematic; Roundup Ready alfalfa would help. Velpar and Sencor dormant applications provide some dandelion control. The weeds reduce crop vigor and yield and will fill areas where stands are not thick and vigorous.