	Oklahoma State University Stillwater, OK
Oklahoma Alfalfa Oklahoma Cooperative Extension Service Oklahoma Agricultural Experiment Station

Weed Control in New Stands

For fall planted alfalfa, it is important to plant in early September on a good seedbed. The first step to be assured of good stand life for the field is to start off with a good stand in the entire field. Weeds in new stands are a major concern because they compete with alfalfa seedlings for nutrients, water, and light. They also can reduce forage quality and yield of first harvest.

Herbicide Options Include:

Eptam^Ž must be applied before planting alfalfa and properly incorporated. Incorporation is best done when the soil is dry. Herbicide loss can result if soil is wet at time of incorporation. Can expect good control of grasses and broadleaf weeds like henbit, but not that effective on pigweeds and mustards. This means that Butyrac^Ž 200 will most likely need to be applied to control pigweeds in spring planted alfalfa, since most producers have pigweeds in their fields.

PPI herbicides are usually not recommended for fall planted alfalfa because:

Incorporating herbicides can ruin a good seedbed and delay the establishment of alfalfa. This is a major problem when moisture is limiting like it is in August of many years.
Most producers do a good job of preventing seed production of weeds in previous crops. So, weeds are not normally a problem.
Cool-season weeds in fall-planted alfalfa seldom prevent establishment of seedling alfalfa plants.
The dinitroaniline PPI herbicides (such as Balan^TM) are not very effective on wheat and cheat, the two main weed problems.
Good postemergence herbicide options are available if weed infestations merit treatment.

Butyrac^Ž 200 (2,4-DB)is an auxin herbicide that is very similar to 2,4-D. Weeds such as pigweeds metabolize 2,4-DB into 2,4-D and as a result are killed. Alfalfa does not do this, so it is tolerant to 2,4-DB. Do not use 2,4-D on alfalfa since it will kill it. 2,4-DB is only effective on broadleaf weeds like pigweeds and mustards when they are small (less than 4 inches tall) and actively growing. It is important to control cool-season weeds in the fall for best results.

Spring applications of Butyrac^Ž 200 are not very effective on broadleaf weeds such as shepherdspurse, henbit, and chickweed, but can be effective for control of cutleaf eveningprimrose.

Poast Plus^Ž is a nonresidual herbicide that can give good control of most small emerged annual summer and winter grasses. It is essential that 1 quart of crop oil concentrate/acre be added to the spray mix. It is important to use the rate listed on the label for the various grasses.

Both Butyrac^Ž200 and Poast Plus^Ž are translocated herbicides, so weeds need to be actively growing (good soil moisture and temperature) when applied. Poast Plus^Ž and Butyrac^Ž are often mixed together as a spray mixture when both broadleaf weeds and weedy grasses are a problem. It is important to use two pint rate of Butyrac^Ž 200 in the mixture since the crop oil used in the mix increases appears to increase the activity of Butyrac^Ž, thus too much injury to alfalfa could result at higher rates.

Jim Stritzke
Former Alfalfa Weed Control Specialist
Department of Plant and Soil Sciences
Oklahoma State University

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