Scout for and Create Weed Maps before Soybean and Sugarbeet Harvest

This page was adapted from the article, "Scout for and Create Weed Maps before Soybean and Sugarbeet Harvest," which appeared in Crop & Pest Report on September 22, 2022

In some years, weeds emerge simultaneously with crops causing weed interference in corn, soybean, wheat and sugarbeet. Unfortunately, weed escapes have been evident in wheat and are evident in soybean and sugarbeet (waterhemp towering over sunflowers has been observed). Even after wheat has been harvested, there is still time to scout for and map weedy patches in soybean and sugarbeet fields. You may also elect to draw maps of localized areas in fields you wish to avoid harvesting due to high weed density.

Draw weed maps and document the two or three most prevalent weed species in fields. ‘Dropping a pin’ using the combine GPS mapping system as you travel through a weedy section at harvest is easy and provides useful information about the distribution of weeds in fields. Many growers have their own drones or have access to drones. Use them to collect images or video footage of the crop that can be viewed or analyzed to identify high density weed patches. I consider weed maps, especially spatial maps collected annually to be field records just as valuable as yield monitor data.

It might be worth collecting seed and conducting a resistance test, If weed control from herbicides is less than expected. The NDSU and UMN sugarbeet team is especially interested in monitoring fields or geographical regions were common lambsquarters and common ragweed was difficult to control, especially in sugarbeet. Dr. Debalin Sarangi is actively tracking herbicide resistance in Minnesota. In addition, there are instances where preemergence chemistry may not have met your expectations. It is not inconceivable that there could be resistance concerns with soil residual herbicides.

Don’t collect seed too early for a resistance test. A good quantity of viable seed is needed for testing. The most common problem is collecting immature seed by stripping seed from the head rather than mature seed which you can brush off gently. Common ragweed is especially difficult to work with and needs to be mature before harvest. Make sure sample is fully dry and stored in a paper bag as moisture may cause the sample to rot.