Weed Management

Lambsquarters

Weeds are dynamic and adaptable and require a diversified approach for long-term management. Good weed control occurs from pre-plant to post-harvest..

Crop rotation

Practice crop rotation to control those weeds that may be easier to control in rotation crops than in soybeans. The major goal during the rotation year is to reduce the number of weed seed available for germination the following season. If the full benefit of the rotation is to be achieved, weeds must be controlled throughout the growing season of the rotational crop. Rotating crops will give you the added benefit of reducing populations of many insect, disease, and nematode pests.

Crop competition

Crop competition is one of the most important, but often overlooked tools in weed control. The plant that emerges first and grows most rapidly is usually the plant that will have the competitive advantage. Therefore, do everything you can to ensure that the soybeans, and not the weeds, have this competitive advantage. This involves good agronomic practices such as choosing a well-adapted variety, good fertility, maintaining proper soil pH, adequate plant populations, and using row spacings as narrow as practical.

Cultivation

Cultivation is a good and economical method of weed control. Cultivate when weeds are present, but still young. Cultivate only deep enough to achieve weed control, since deep cultivation may disturb soybean roots, bring weed seed to the surface, and disturb the layer of soil previously treated with a herbicide, if one was used.

Identify weeds before tilling for weed management. Are they annual weeds or perennial weeds? Culitvation is not recommended for perennial species because they can be spread by cutting below-ground tissue.

Mechanical tillage is an important component of weed control on organic farms. See Weed Control for Organic Farmers from Iowa State University (3 MB pdf file).

Herbicides

Herbicides are an effective tool for weed control in soybeans. Choose your herbicides based on the specific weeds present in your fields. Use the full recommended herbicide rate and proper application timing for the hardest-to-control weed species present in the field . Scout fields after herbicide application to ensure control has been achieved.

Since the introduction of Roundup Ready® soybean in 1996, many growers rely on Roudup and other herbicides containing the active ingredient glyphosate. Glyphosate provides control of both broadleaf weeds and annual grasses. An important practice to slow or avoid the development of resistance to glyphosate is to reduce the number of times glyphosate is used, which can be done by rotating herbicide modes of action. This can be done by using other materials in corn and then using glyphosate in soybeans, and/or using a preemergence herbicide followed by glyphosate in the same season. Preplant or preemergence herbicide treatment combined with cultural practices and cultivation is a good strategy to ensure that the soybeans have the initial competitive advantage over the weeds.

Be sure to rotate products with different mode of action within the season and between seasons, including the rotation crops. Use a herbicide mode of action chart to help you choose different materials. The active ingredient will be listed on the herbicide label. View Herbicide Mode of Action chart in pdf format»