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Agronomy Update

Post Weed Control in Soybeans

Published on Friday, June 3, 2016

By this point in the season, farmers are looking to control weeds that have emerged following a break in residual activity. When making a weed control plan, there are several things to keep in mind. Check out the video below to learn more.

Weed Identification is Important

Weeds of concern this season include

  1. Marestail:
    • Marestail is best controlled with a burndown application, but some marestail may not have been controlled due to the weather we experienced during planting.
    • Marestail can be identified by its bristly leaf hairs and upright stance.

  2. Giant Ragweed:
    • Giant ragweed will have penny sized cotyledon leaves if identified early.
    • Once the weed has gained some size, the leaves will have three points, or lobes.

  3. Common Lambsquarter:
    • Common lambsquarter will have triangular shaped and sometimes have a white powdery look to them.
    • The leaf margins may also be purple.

Controlling Weeds During Critical Periods

For soybeans, the critical period of weed control lasts from V1 until R1. Not controlling weeds during this time period can result in a decrease of 5 percent or more in yield. For this reason, we suggest farmers control weeds at a height of 6 in. or less. By controlling weeds early, you increase the effectiveness of your herbicides and decrease the impact weeds will have on yield.

Herbicide Options Based on Weed Populations

In the state of Ohio, if marestail is present then glyphosate and ALS resistance is assumed. In the case of giant ragweed, there is also the possibility of glyphosate and ALS resistance. Remember, resistance can limit your herbicide options. If you are experiencing problems with these weeds, you may want to consider one of the options in the chart below. 

Don’t hesitate to reach out with any questions or concerns regarding weeds in your fields.

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Alex Knight

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