Growers Hear Weed Control Strategies in Middlebury
Published: Friday, March 6, 2026
Farmers should be careful not to let waterhemp get a foothold in their fields, according to a Purdue University weed scientist. A few weeds one year could result in thousands the next. That's how quickly waterhemp can multiply.
Speaking at a Purdue Crop Management Workshop in Middlebury, Tommy Butts showed a slide of a Northwest Indiana soybean field with only two waterhemp plants in it. The next year, the field was planted to corn and the waterhemp exploded.
"Those two lone, little waterhemp plants all of a sudden turned into two massive patches of waterhemp plants," he said. "You carry that out one more year and all of a sudden you've got a mess on your hands."
Butts urged crop growers to move away from a short-term management approach in which they "spray, spray again, maybe a third time and hope for the best."
"With stuff like waterhemp, and giant ragweed for that matter, we've got to start looking at it from a long-term approach," he said. "We can't just keep spraying, spraying and every year we start new again. We have to look at it from a long-term standpoint."
Looking back at 2025, the early part of the growing season was wet and cool. There were many instances in which corn and soybeans suffered herbicide injury because they couldn't break down the herbicide like they were supposed to.
"In a normal year, if we have some heat, we'll never see this," he said, referring to a slide showing herbicide injury to a soybean plant. "It will grow out of this."
Ninety percent of the time, corn and soybeans plants will recover and yield well.
"Don't let the weather conditions scare you away from using residuals and using full label rates for your soil types for those residuals," Butts said.
Otherwise, he added, waterhemp and ragweed will "eat our lunch."
Once the cool, wet weather ended, mid-summer was hot and dry. Residual herbicides couldn't activate and "really didn't do anything." Butts said residuals need about a half inch of rain to activate.
Based on rainfall data from 2004 through 2024, Butts said the first half of May shows good chances (60%) for every day. However, that daily precipitation chance drops to less than 50% during the second half of May. The dry spell continues into June, with 50% chances through the first half.
"So, there's a whole month of time in there—second half of May and first half of June—where it's a coin toss on whether we're going to catch the activating rainfall or not. That's rough."
According to Butts, that's the same window when farmers are trying to spray herbicides.
"If you have irrigation, use it," he said. "That will activate residuals just like a rainfall will."
A second option is to be more precise in herbicide selection.
"What I mean by that is there are certain residual herbicides that are active at lower rainfall amounts," he said.
One example is dicamba, which is "really, really good" in dry conditions.
Butts recalled some of the herbicide complaints from 2025. He received a lot of calls on products not being effective against waterhemp.
"The scariest one to me that came out of 2025 was we had a lot of calls and emails on Mesotrione or Callisto, plus Atrazine, failing in our corn acres."
Five years ago, those herbicides "smoked everything," Butts said. However, they appear to have lost some of their efficacy over the years.
Butts also reported hearing some complaints about auxin herbicides in corn and Liberty and Enlist in soybeans.
Part, but not all, of the failures were due to the cool, wet conditions, he said, as auxin herbicides and Liberty don't perform well in cool, wet conditions.
But the weather is only part of the reason. The other part is resistance.
"We haven't fully confirmed both dicamba and 2,4-D resistance in the state," he said. "We for sure have 2, 4-D resistance in the state."
Meanwhile, data from several other major crop states is pointing to resistance for dicamba.
"Basically, auxins go hand in hand with each another when it comes to resistance," he said. "When you lose one, you kind of lose them all."
Butts said he is hearing reports of resistance to Calisto and Atrazine.
Waterhemp is showing resistance in some states—not Indiana—to Group 15 herbicides like Dual, Acetochlor and Zidua, according to Butts.
"They have a mess on their hands in Illinois with Group 15 resistance right now," he said. "The wind blows west to east most of the time. It's only a matter of time until that blows over here and we're dealing with that too."
He advised growers to rotate their use of chemicals, with different modes of action, within the Group 15 product list. He said that will prolong the Group 15 technology.
Prowl shows 60-70% control on waterhemp, Butts said, but it's more effective when used with other chemicals.
"The main message on this is you've got to throw different things at it in different combinations," he said. "There's no relying on a single herbicide by itself that's going to get us out of this."
On waterhemp, farmers can't wait for the next new, more effective herbicide to be introduced in one or two years. The pipeline is "very scary" right now, with only three new chemicals coming to market.
His overall message to growers is to look at weed management from a long-term standpoint.
"It's taking the whole toolbox and picking and choosing different pieces and putting it together in this program," he said.
One item in the toolbox is how the seed is put in the ground.
"We need to start picking production practices that can hopefully increase canopy development. If we can go to narrow row widths, that is a huge benefit from a weed management standpoint."
A dense canopy casts a shadow on the ground and discourages weed development.
Butts advised growers to plant as early as possible, before waterhemp germinates.
"Waterhemp likes heat," he said. "It comes on late. If we get the crop planted earlier and get it up and growing, we start to get that canopy sooner and it has a competitive advantage because it's already up and growing."
Another item in the toolbox is cover crops.
"Cover crops can help a ton by suppressing our different weed species, particularly some of those later emerging weeds," Butts said. "It helps get rid of at least the first flush or the second flush."
The toolbox includes four items: cover crops, narrow row width, herbicides and tillage, when necessary.
"Some of the data we have shows that if you do a deep tillage once every four or five years, particularly with waterhemp, which germinates in the top half inch of soil, if you take that and bury that 6 inches down or more, it can't come out of the ground," Butts said. "It's only viable for about five years or so. About 95% of that seed bank you can eliminate in that five-year time period by burying it deep."
In addition to all these tools, Butts said growers should clean their equipment after every field and combine weedy fields last.
"Thinking long-term, the more that we can manage weed seed, the better off we're going to be," he said.
Butts wrapped up his presentation by discussing control methods for another problem weed, burcucumber.
"The spray drone actually was pretty effective at knocking this out," he said. "The main concern on the spray drone is consistency across an entire field, but if it's burcucumber and you're just trying to hit patches or something, this seems like a really good option so you don't end up with a jungle of vines tied up on a sprayer."
Butts advised two applications for effective control of burcucumber in corn, one at dent and another at black layer.
At the dent stage, Accent killed the vegetation and knocked out seed production. However, the label requires a 70-day preharvest interval. Butts said that puts it within the harvest window for corn.
At the black layer, Paraquat was effective at killing vegetation right before harvest. However, Paraquat doesn't affect seed production.
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