In the constant battle to keep soybean fields clean, few weeds have proven as difficult for farmers to control as waterhemp.
"Last year, in 2025 we struggled a lot with waterhemp, and that's a weed that's going to continue to present problems for us," notes Mike Hannewald, field agronomist with Beck's Hybrids.
Seasonlong competition by waterhemp (more than 20 plants per square foot) has been shown to reduce soybean yield by 44%. Waterhemp emerging as late as V5 soybean reduced yields up to 10%, according to Take Action.
Hannewald's message to farmers for 2026 is this: Controlling waterhemp isn't about a single product or pass. It's about designing a thoughtful, layered herbicide program that starts before the planter rolls.
Here is a summary of the four key practices he recommends:
1. Begin the season with clean fields.
The first principle is deceptively simple: start clean.
Hannewald advises using a burndown herbicide pass or properly set tillage if you're in conventional tillage to completely remove existing weeds before planting.
2. Use a "three in the pre" herbicide application
Beck's Practical Farm Research (PFR) data shows when three modes of action are used in a pre-emerge application to control waterhemp, 97% control was achieved and maintained 45 days after treatment.
"That residual can be either made after we do our tillage or combined with our burndown pass," Hannewald says.
Because there are many active ingredients available - and even more brand names - it's easy to not succeed in getting three different chemistries in the tank. To help minimize confusion, Hannewald recommends tuning into the chemistry group numbers.
He recommends soybean growers use some combination of three herbicides from these four groups:
Group 2: Amino acid synthesis inhibitors, such as cloransulam.
Group 5: Photosynthesis inhibitors, such as metribuzin.
Group 14: Cell membrane disruptors, such as sulfentrazone
Group 15: Seedling root growth inhibitors, such as metolachlor, acetochlor and pyroxasulfone
"Now, if you are planting XtendFlex soybeans and you're using an approved version of dicamba as your burndown, dicamba does have residual value, so that counts as one of the three," Hannewald says. "But if you're using 2,4-D on Enlist soybeans, 2,4-D does not have residual value, so that doesn't count. You need to add three additional modes of action there."
3. Make a post-herbicide pass prior to flowering
If building a strong pre strategy is partly about chemistry, the next step-timing the post pass-is about mindset. For many soybean growers, waiting to spray until weeds are obvious is a common course of action. Hannewald believes it's time to change that thinking.
"This is the biggest mindset shift for us to stay ahead of waterhemp, and that's spraying your soybeans before flowering," he says.
In practical terms, this means moving the post pass much earlier than many farmers are used to-often when the field appears relatively clean (e.g. around V3 rather than R1).
"In most cases, you're probably going to be driving through the field thinking, 'I don't need to be out here at this point because there's not much weed pressure, if at all,'" he says.
But targeting small weeds early, before the beans canopy, allows you to get good coverage and control. This is especially important if you're going to spray glufosinate (Liberty), reports Isaac Ferrie, Crop-Tech Consulting field agronomist.
According to the label Liberty can be sprayed on LibertyLink soybeans from emergence up to the R1 growth stage (first bloom).
"That means once 50% of those plants out there have one flower on them, we can't spray Liberty," Ferrie says.
Another consideration is the impact of later herbicide applications on yield potential.
A PFR study that compared herbicide applications in soybeans at V3 to those made at R1 found the latter application caused a yield decrease.
"We saw losses of 1.2 bushels to 2.5 bushels per acre just from the R1 application stressing that soybean plant," Hannewald explains. "Even though our beans are tolerant to these herbicides, it still takes energy for that soybean plant to process that herbicide, metabolize it, break it down and get rid of it, and that energy causes stress on the plant."
4. Add an in-season residual with the post pass
Step four is adding an in-season residual to the post pass. This is what makes the early post pass work.
"At this point, we still have some soil visible, and when we add that in-season residual, it's like you're laying a blanket across that soil to stop late-emerging waterhemp from growing," says Hannewald.
He adds that he likes using a Group 15 herbicide as the residual now, because they're effective on small-seeded broadleaf weeds.
Hannewald says Beck's PFR shows farmers get 6% additional control – going from 88% to 94% control of waterhemp at harvest – by adding the in-season residual.
"While 6% may not seem like a whole lot, that works out to 17.1 million fewer viable waterhemp seeds per acre going in our seed bank for the next year and future years," he says.
In summary, Hannewald boils his recommendations for 2026 down to a four-step framework: start clean, layer three modes of action into the pre pass, move the post application earlier-before flowering-and add an in-season residual to carry the field through canopy and into harvest with fewer waterhemp.
