Mastering Soybean Weed Management: Six Observations from 30 Years of Field Research
When it comes to managing weeds in soybeans, few people have seen more than Dr. Peter Sikkema. After three decades of research, he’s learned exactly how early weeds steal yield, how fast losses add up, and what actually works when it comes to tough species like Canada fleabane and waterhemp.
During a 2025 FMC Tech Talks webinar, he broke his findings into six observations with clear strategies that soybean growers can put to work right away.
1. Waiting to Spray Costs More Than You Think
Sikkema’s biggest message was also the simplest: don’t wait. Even a few inches of weed growth can have a big impact. By the time weeds hit a height of 8 inches, losses can reach $171/acre – that’s over $42,000 on a 250-acre soybean field. A lot of this comes from relying only on a late post-emergence spray. It might feel efficient to wait to spray until weeds have emerged, but the hidden yield loss can be huge.
2. Start Clean, Stay Clean
After years of side-by-side trials, Sikkema found that a two-pass program consistently outperforms anything else.
A soil-applied pre-emergence application followed by a post-emergence spray:
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Reduces early weed pressure and protects the crop during critical early growth stages
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Gives more flexibility on timing and improves the performance of the post-emergence application
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Reduces weed seed return to the soil
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Decreases the selection pressure for the evolution of herbicide-resistant weeds
One trial saw yields jump from 39 bu/ac to 51 bu/ac with a two-pass approach. That’s a strong reminder that an effective pre-emergence application is essential for achieving top yields.
3. Canada Fleabane: Handle It Early or Fight It All Year
If there’s one weed that can sink a soybean crop, it’s multiple herbicide-resistant Canada fleabane. In severe cases, it can cause up to 99% yield loss. And once soybeans are up, post-emergence options do not provide acceptable control.
For IP and Roundup® Ready beans, Sikkema found the most consistent results with a pre-emergence application of Roundup® + Eragon® + metribuzin. For Xtend soybeans, a tank-mix of Roundup® + dicamba + Eragon® provided the strongest control. And for E3 systems, pairing Roundup® + EnlistTM + Eragon® gave the strongest and most reliable results.
4. Waterhemp Requires a Foundation
Waterhemp isn’t going away and it spreads fast. But Sikkema’s research shows that a strong soil-applied herbicide can make a big difference. Products like Authority® Supreme herbicide delivered 80%–95% control before the soybeans even emerged.
But pre-emergence isn’t enough on its own. The best results — up to 100% control —came from an effective pre-emergence application followed by a timely post application. That combination limited the number of escapes, reduced the weed size at post application timing, and provided the post-emergence products the best chance to work.
5. Effective Weed Control Delivers a Huge ROI
Even with tighter margins and lower soybean price projections, an effective two-pass weed control program is one of the best-returning investments a grower can make. Sikkema calculated an average 446% return over recent years, and even with lower projected soybean prices, ROI is expected to remain just under 400%.
6. A Clean Field at Harvest Doesn’t Tell the Whole Story
One of Sikkema’s more surprising findings was that a clean field at harvest doesn’t always mean the grower got the most out of it. Two fields might look identical in September but differ by 3.3 bu/ac in yield simply because one grower stayed ahead of early-emerging weeds and the other did not.
Why Authority® Supreme Herbicide is a Fit for Growers Who Want to Get Ahead
The take-home message from Sikkema’s research is that the most successful soybean growers protect their crop early and implement an effective two-pass weed control program that starts with a broad-spectrum soil-applied herbicide.
That’s exactly where Authority® Supreme herbicide fits. With its Group 14 + 15 combination, it provides powerful early-season control of both broadleaf and grassy weeds, including tough, resistant species. It also delivers the extended residual activity needed to keep fields clean through the critical weed-free period, setting you up for stronger yields and greater ROI.
Whether managing IP acres or herbicide-tolerant systems, Authority® Supreme herbicide gives you a dependable, field-tested foundation, one that truly makes the first pass the best pass.
Enlist is a trademark of Corteva AgroSciences. Eragon is a trademark of BASF Agricultural Solutions Canada. Roundup is a trademark of Bayer Group.