This is the second article in a four-part series about three of UW-Madison’s Agricultural Research Stations. The pieces are by Chris Barncard, UW-Madison Strategic Communications. Photos by Michael P. King, UW–Madison College of Agricultural and Life Sciences.
Waterhemp is a stubborn type of pigweed that crowds out and robs nutrients from corn and soybeans. It has a particular knack for outfoxing the chemicals designed to kill it — developing resistance to herbicides almost as fast as they can be approved for use. Five or six years ago, 10% of the waterhemp Rodrigo Werle encountered was resistant to some of the herbicides commonly used for weed control in corn and soybean fields; in 2023, it was already up to 50%.
“Relying on chemistry alone is not sustainable because of that speed,” says Werle, an associate professor and extension specialist in the UW-Madison’s Department of Plant and Agroecosystem Sciences.
That’s where Werle and Daniel Smith, a crops and soils program manager in the UW Division of Extension, come in. Since 2018, corn and soybean fields at the Lancaster Agricultural Research Station in southwestern Wisconsin have been home to an experiment comparing different weed management practices side by side, from the most conventional tilled soil sprayed repeatedly with herbicides to no-till plots that cut back deeply on spraying in favor of cover crops — in this case, a winter hardy grain called winter rye that can be planted in fall after corn or soybeans are harvested.
The differences are stark. The tilled rows, where the soil has been turned over each year, sit noticeably lower, the soil washed away forever without plant roots to retain it. And there’s waterhemp. Even after fresh applications of herbicide, many of the weeds are hanging on with little damage.
In contrast are the rows where Werle and Smith have let the winter rye grow right up to the moment farmers “plant green” — planting rows of corn directly into the still-thriving cover crop. Then they kill off the rye with a single application of an herbicide, which doesn’t bother the corn. Organic farmers could use a roller crimper machine to kill the rye without an herbicide.
“Where we’ve grown winter rye as a cover crop, you can see that there’s hardly any weeds,” says Smith.
That’s because what’s left of the cover crop becomes biomass, which acts like a mulch on top of the soil, reducing erosion and keeping the surface at a more consistent temperature.
“The mulch buffers temperature fluctuations and tricks the weed seeds into not germinating,” Werle says. “It’s fascinating.”
And it’s effective. With just one herbicide application to “terminate” the rye cover crop — more time- and cost-effective for farmers than repeated spraying — Werle and Smith are seeing little to no waterhemp develop, compared to the lasting problems in conventionally tilled corn plots that get repeated herbicide applications. The approach is even more successful in soybeans. And, by reducing herbicide use on the waterhemp, farmers give the weed fewer chances to develop resistance to the chemicals.
Hundreds of farmers have seen the results during open-house-style “field days” at research stations where Werle, Smith, and other researchers can quite literally walk them through the experiments. It’s a chance for crowds of growers to step through rows of cover crop examples, herbicide trials, new technology demonstrations, and, for experienced farmers like Jake Kaderly, to pepper Werle with questions.
“In the old days, herbicides worked on everything,” says Kaderly, who farms near Juda, Wisconsin, and works as an agronomist advising other farmers. “But nature adapts and overcomes, so we need to find ways to stay ahead.”
His clients, though, are often reluctant to shift away from practices they’ve grown comfortable with, even as those practices become less successful.
“It’s not easy to talk about these things if it’s not the way their farm’s been working for years,” Kaderly says. “You’re not going to consider a change if it feels like a risk. Well, in Rodrigo’s research fields, you can see it working. You see the proof.”
Stay tuned for Part 3, featuring the Arlington ARS.
