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Narrower rows, early-season action can improve weed management

Article cover photo
A farmer scouts a field that was impacted by herbicide resistant weeds last summer near Jefferson. Herbicide resistance continues to be a threat to profitability for farmers across the U.S. (Photo: Joseph Murphy/Iowa Soybean Association)

By Aaron Putze, APR

(Editor’s note: Interested in learning more about herbicide resistance and improving weed management? The ISA Farmer Research Conference, Feb. 6-7, in Des Moines will feature several presentations on the issues including a keynote by Kevin Bradley of the University of Missouri. Learn more and register now at

Second in a three-part series

Herbicide resistant weeds are appearing on more row crop acres in Iowa, reducing soybean yields and income potential for farmers already financially stressed by sinking commodity prices.

While eliminating resistance entirely is impossible, experts agree the adoption of more effective management practices is critical to keep farmers one step ahead in the annual race against weed infestations and lost productivity.

The frank assessment received unanimous agreement during a discussion by a panel comprised of agronomists, scientists and farmers held January 10 at WMT Radio’s annual Ag Expo and Crop Fair in Cedar Rapids. But opinions differed on the most effective techniques to win the escalating war against weeds. 

In the second of a three-part series, Tony Pleggenkuhl, regional sales agronomist, Stine Seed, John Cantwell, farmer and weed management technology development representative, Monsanto and Kent Bennis, marketing specialist and farmer, Dow AgroSciences, offer their perspectives of the proliferation of herbicide resistance, management resources and production techniques to mitigate yield-robbing weed infestations.

Tony Pleggenkuhl

We’ve seen herbicide resistance expand further and further north – from south of I-80 to now north of I-80 and into southern Minnesota. Easy herbicide programs and using the same product year-over-year has contributed to this movement.

The biggest thing we’ve got going for us is the number of tools available to manage weeds. The challenge is not abusing these tools in a way that puts us right back at the start of dealing with weeds.

I encourage farmers to put down a residual early on, vary modes of action throughout the year and consider post-emerge herbicide options. You also must vary chemistries. In the past, it was easy to knock down 3-foot weeds but that has caused problems and is no longer effective. If we don’t vary chemistries, we’ll be battling the same, if not worse problems, in a few years than we are today.

From the soybean perspective, the chemistries are a bit more detrimental because they can cause some yield drag. Glyphosate didn’t cause those issues which is why it became so popular. Be sure your weed population doesn’t get out of control. We develop tolerance when weeds get tall and they’ve hardened themselves to chemistries.

As an agronomist, record keeping is a critical part of my work. Keep track of where you have the weed pressures on your acres. It’s difficult to keep it all straight year-over-year and as your crop rotation changes. Develop a game plan in early winter. Sure, it never goes like clockwork over the course of a growing season but having a plan helps get you off to a good start. Then adapt as weather and other factors dictate.

John Cantwell

Weed control in row crops went from very complicated in the 1970s to simple in the late-1990s and 2000s. Now, it’s complicated again.

We used to go with 30-inch rows because we depended on mechanical control. Then we went to a two-pass approach and the cultivators went away. Staying with the 30-inch rows have given our weeds a good start in the spring. Weeds don’t like shade. When we allow them to have sun, they germinate quicker. If you’re clinging to 30-inch rows, your chemistry costs will be higher. Clearly, when you look at 15-inch soybeans rather than 30, you’re going to need more residuals and knock-down chemistries. Does your 30-inch row make sense? Or should you invest in a second planter? Farmers who have adopted narrow-row soybeans are getting along much better in controlling weeds.

By mid-January, we begin to lose the pre-pay options with chemicals. I’ve got to have a marketing plan in 2018 because of low prices. If you’ve had trouble with weed management, you’re going to need a plan for managing weeds, too. Three-dollar-and-ten-cent corn with 280-290 bushels-per-acre coming through the combine is the place to start as you put pencil to paper and calculate income and expenses. Put a plan together and make sure it sticks. If you can’t get those early chemistries down, then have a second option in mind so you can move quickly when there’s a chance between weather events.

Dicamba may be an important part of your plan. Every farmer that had an issue last year with dicamba received a visit from a representative. Chemical trespass is a bad thing and we can’t let it happen. There have been changes made to the label and training sessions are being held statewide. Take advantage of them. We have to do better with the chemistry and we will. 

Kent Bennis

There was an easy button in our industry for weeds for a while and we abused it over time. We’re going to see quite a shift as we move into the new technologies. Moving forward, there will be restraints on how and when we use these treatments. It’s going to cause some conversations – and we need to have them – regarding how we act on this issue.

The best way to have clean soybeans is to have really clean corn the year before. We have solid good options for managing weeds in corn and rarely see problems. We need to continue this and make sure we keep the weed bank down on the corn acres.

The chances of having to respray in July is much higher when you have 30-inch rows. Keep the field clean through mid-June. Then, on June 21, spray glyphosate to go to work through July 3 and then you’re done for the year. The most important day in the crop year is June 21. The days start getting shorter and the beans realize that they need to get growing. Weed germination after June 21 also changes dramatically. With the new technologies, they need to be put on before R1; you need to be done by June 21 and some states have gone to June 20 when you have to be done spraying with the Xtend system. Be really mindful of those dates and the importance of getting to weeds early while the beans are still deciding to grow.

Row spacing matters. If things are running smoothly on your farm, then consider narrow-row corn. That’s a good way to manage weeds and expenses more effectively. If you can move from 30-inch to narrow-row corn and soybeans without the yield drag, that’s optimum. We need to get these beans into rows narrower than 30 inches. So how do you move to narrow rows with corn and move herbicide treatments up earlier in the year? Calculating these expenses and then determining how best to utilize your resources to optimize yields while managing a seed bank that doesn’t seem to want to shrink – that’s the challenge.

Editor’s note: The last of the three-part series will feature the observations of Jennifer Horning, FMC Retail Marketing Manager, Brian Wischmeier, Herbicide Tolerant Specialist, Dow-DuPont Pioneer and Kurt Maertens, BASF Technical Services Representative.

For media inquiries, please contact Katie Johnson, ISA Public Relations Manager at or Aaron Putze, ISA Communications Director at

For permission to republish articles or to request high-res photos contact Aaron Putze at Iowa Soybean Association | 1255 SW Prairie Trail Pkwy | Ankeny | IA | 50023 | US

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