Battle of the Weeds: Why Even Letting 6% of Late Season Weeds Escape Eats into Corn Yields

Planted on the south side of the University of Illinois campus are fields yielding fruitful research for farmers.The research farms through the Department of Crop Sciences have looked into ways to improve various corn hybrids through nitrogen use efficiency as well as herbicide research that have attracted even more attention over the past five years.

“Our primary work that we do here in the herbicide evaluation program is to look at various types of products
that are in the marketplace, or some that soon will be entering the marketplace, and try to determine what fit
that they do have, what is their spectrum of control, and more,” says Aaron Hager, associate professor of Extension weed science in the Department of Crop Sciences, University of Illinois. 

Primarily digging into corn and soybean production, small grains are also producing key findings in the Champaign, Ill., fields, as researchers have harvested data that’s now decades deep. The fields are also a second home to Hager, who has been wading through the same fields for nearly 30 years.

“Years ago, the person who was running the evaluation program, Mr. Doug Maxwell, used a software program that allowed all these data to be archived and stored for many, many years,” says Hager. 

Meeting of the Minds 

While the data is useful every year, it’s three decades of information, that stacked up, is nearly untouched.

“Dr. Hager is just two doors down from my office, and we’ve had some great conversations over the years,” says Marty Williams, ecologist with the USDA Agricultural Research Service (ARS), who also holds a faculty appointment with the University of Illinois Department of Crop Sciences. “It was a number of years ago, we had a conversation about making use of larger datasets. It's pretty intriguing thinking about having hundreds of environments, if not thousands of environments, to get a better understanding of weather variability on crop production. And we finally found the right student, Chris Landau, who just got his Ph.D. in May, and he delivered for us in a big way with this particular dataset.”

The focus of the research was what affect climate change would have on weed species found right here in Illinois. “We looked into what would an atmosphere enriched with CO2, for example, would that more favor weed species,” asks Hager.

Hager says just homing in on one or two years of data doesn’t paint the bigger picture on trends that have been taking shape over the past 30 years. 

“We've seen waterhemp in the past 25 years, really expand its range across Illinois,” Hager says. “Now, was  this all climate change? Or was this something else? Well, we really don't know for sure what component each of these various factors play. But we've taken the species that literally 30 years ago hardly anybody recognized in the state of Illinois; it’s indigenous and has always been here. But now we can find that virtually in every one of Illinois 102 counties.”

Late-Season Weeds Eat Into Final Yields 

By digging through the thousands of data sets, and then analyzing factors like weather, yields, what weeds were present and more, the team uncovered one important finding.

“What we found most recently was that incomplete weed control exacerbates corn yield loss due to adverse weather, particularly dry or hot conditions around corn silking,” says Williams.

On a scale of zero being the worst and 100% being the best, Williams says even 94% weed control can produce problems.

“It doesn't take many out there to cause a major problem and have a major impact on the corn yield, particularly at these important growth stages of the crop right around silking with adverse weather,” Williams
adds.

Even as the University of Illinois is already coordinating with other pools of data from land grant universities across the country, Williams says he hopes this research motivates additional innovation and technology to create change. 

“I think this sends a cautionary alarm that weeds are not getting easier to manage, and with the kinds of weather we're headed into these are exactly the kinds of conditions where incomplete weed control will actually exacerbate corn yield loss,” William adds. “So now's the time to act, now's the time to come up with new ways of managing weeds.”

The Weather Wildcard

As weather plays a role in weed control, Hager says it’s something growers will continue to battle.

“I think it's pretty safe to say that weeds are going to be able to adapt, whether it's to changes in the climate or changes into how we're trying to manage these, they're  weeds for a reason,” adds Hager. “They're very adaptable, they have a great deal of plasticity in how they grow, they will figure out a way through the evolutionary process to survive to reproduce.” 

As weeds continue to adapt to climate, weed scientists continue to stress the importance of moving away from a single approach to combatting weeds. 

“Simply opening up a new jug if a new product comes into the marketplace is going to continue to repeat what we've done historically in the past,” says Hager. “So, trying to maybe move the goalposts to thinking about what else can we do to try to ensure that by the end of the growing season, that there's no weed seed that's added back into the soil seed bank? And ultimately, that's the victory. That's the win.”