Indiana Prairie Farmer publishes a column written by Tom Bechman with the help of CCAs for CCAs and their clients. With permission from Prairie Farmer we are posting these Soybean and Corn Pest Beat articles on the CCA website. Many thanks to the authors and the support of Indiana Prairie Farmer.
Soybean Pest Beat Articles
Tackle top 2 weeds in soybeans
The Indiana Certified Crop Adviser panel includes Steve Gauck, an agronomy manager for Beck’s, Greensburg; Jeff Nagel, agronomist for Keystone Cooperative, Lafayette; and Marty Park, agronomist with Gutwein Seed Services, Rensselaer.
Giant ragweed and waterhemp are currently public enemies No. 1 and 2 here. How can we get a jump on both these weeds this year?
Gauck: The challenge with these two weed species is the fact that one is a large-seeded broadleaf and the other is a small-seeded broadleaf. This means they both require slightly different programs to maximize control. Many herbicides do not control both, so you need multiple modes of action in your herbicide program.
Start with your planter. Narrow row soybeans planted early will canopy faster and be the best weed control option for both species. Next, utilize an integrated approach: Apply effective pre-plant burndown, use multiple effective residual herbicides at planting, and make your post application of herbicide 24 to 28 days after soybean emergence to ensure timely control.
Nagel: These two weeds are the drivers of weed control management in soybeans, particularly waterhemp. Weed management strategy has not changed. Start clean, use a soil applied residual herbicide, spray postemergence herbicides on small weeds, and use a layered soil applied residual herbicide.
The two predominant soybean trait platforms used today are Enlist E3 and XtendFlex. Essentially, you have Enlist One and glufosinate left for post-waterhemp control in soybeans. While Enlist One can provide very good control of waterhemp, there have been more variable results in the field. Glufosinate worked well in 2025, likely due to warmer temperatures and higher humidity, but folks are using higher rates compared to just a few years ago. The tank mix of Enlist One and Liberty Ultra is the best today for E3 soybeans. There are indications from university weed scientist research that we’re on the path of waterhemp developing resistance to both.
That means it is imperative to use a solid soil applied herbicide with at least two effective sites of action and rates. There are several soil applied herbicide options for waterhemp. These include group 15 herbicides like Dual, Enversa, Outlook, Warrant, Zidua SC, and premixes; group 14 herbicides like Authority, Valor, and premixes; group 5 options like metribuzin; and group 3 — Treflan or Prowl. Soil applied options are more limited for giant ragweed. Most giant ragweed populations are resistant to group 2 herbicides like Classic or Firstrate. However, soil applied rates are often higher than post applied rates so suppression can be achieved with a premix containing Classic or Firstrate. Zidua Pro (premix with Pursuit) and Prefix (premix with fomesafen) can also suppress giant ragweed but will break earlier than Classic or Firstrate.
Cultural practices like sub-30-inch row spacing, sufficient soybean stand for early canopy and incorporating cover crops like cereal rye can also help overall weed control.
Park: Giant ragweed and waterhemp are challenging weeds, especially in non-GMO soybeans with fewer herbicide options. Focus on using soybeans with the XtendFlex technology or Enlist technology. Start by planting into a clean seedbed and using effective preemergence herbicides that provide residual activity and different modes and sites of action. After soybeans emerge, scout and make timely applications of postemergence herbicides tank mixed with a residual herbicide for waterhemp. Continue to scout and respray or use other options like a Weed Zapper or hand weeding as needed to clean up escapes. These programs can be costly, but ultimately the most expensive weed control is poor weed control.
Editor’s note: Glufosinate resistance in waterhemp was confirmed in December by University of Illinois and Southern Illinois University Carbondale.
