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Got weeds in your beans? You’re not alone

Got weeds in your beans? You’re not alone

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A patch of volunteer corn in a soybean field.

A patch of volunteer corn in a soybean field.

Editor’s note: The following was written by Seth Naeve, University of Minnesota Extension soybean agronomist, Jared Goplen and Dave Nicolai, Extension educators, for the university’s website Sept. 7.

It’s been a memorable year for Minnesota soybean producers, but mostly for the wrong reasons. Dry conditions were problematic most of the year. Soybean emergence was affected by dry soil conditions in some fields.

Poor canopy development has allowed waterhemp, volunteer corn and other weeds to establish and poke out of the canopy in fields statewide.

Do these weed escapes really matter?

While farmers all strive for clean fields, it is likely that the sporadic escaped weeds had little effect on this years’ soybean yields.

These weed escapes do have an impact, however. Economic impacts can occur at the local elevator as well as thousands of miles away via export markets. These escapes will also exacerbate weed problems in the future if they are able to produce viable seeds.

The good news is that it isn’t too late to keep these weedy plants out of the combine and out of the commodity stream.

Ideally, weeds should be pulled prior to harvest and removed from fields if seeds have been produced. However, this may not be a realistic option in many situations. If weeds are present in patches, consider mowing these areas to isolate the weed seed to a limited area where it can be carefully monitored and managed in subsequent crops.

Impact on exports

International customers of U.S. soybeans, including China, are rejecting soybean shipments carrying more than 1% foreign material (FM). Since FM includes any material that is not soybean seed, weed seed is an important factor. In fact, the limits on FM in soybean imports are focused on weed seed and other crop seeds, like corn.

Weed seed found in shipments will likely lead to rejection of entire vessels. Rejected vessels are extremely costly for the exporter who will certainly turn around and push costs back through the system to the farmer.

Annually, the Naeve Lab at the University of Minnesota analyzes up to 2,000 soybean samples from U.S. producers for a wide range of quality traits, including FM and weed seed. Although FM tends to be very low (about 0.2% on average), around 25% of the samples contain weed seed, indicating famers are still combining plenty of weeds.

Weeds at harvest

Part of the problem is that our common weeds retain seeds until crop harvest, meaning a large percentage of weed seeds pass through the combine. Research from the University of Wisconsin has documented how important combines are in spreading weed seeds.

Of the 31 samples collected from within nine different combines, 97% of them contained viable weed seed. The weed seed most often found included grasses, pigweeds and common lambsquarters.

Sanitizing combines between fields can minimize the spread of weeds. Focus sanitation efforts towards the front of the combine if time is limited. The greatest number of weed seeds were found on the header, followed by the feeder house, rock trap and rotor.

Efforts to produce high-quality, weed-free grain serves a dual purpose. Keeping weeds out of soybean fields and out of combines will help maintain important market access while simultaneously improving weed management.

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