MALTA, Ill. — Aaron Hager has no good news for soybean producers about waterhemp control.

Hager, of the University of Illinois Department of Crop Sciences, was one of several speakers at the recent Northern Illinois Crop Management Conference at Kishwaukee College. “It’s a good idea to revisit recommendations. We offered some four years ago and situations have gotten quite a bit worse,” he said, for beans and waterhemp.

He explained the nuisance weed, which overpowers soybeans, causing yield loss, is creeping northward in Illinois and is showing up more frequently in Wisconsin, Minnesota and Indiana.

“So, the question is, how do you manage a weed population for which there might not be any viable post-emergence herbicide options for control?” Hager asked.

He explained the resistance has been documented to five herbicide classes: ALS inhibitors, triazines, PPO inhibitors, glyphosate and HPPD inhibitors. The bigger problem is that populations, on an individual plant and field basis, are showing resistance to multiple classes of herbicides.

“We can’t just tank-mix our way out of this problem,” Hager said.

He offered a four-step process to reduce the problem, based on research. “The goal is to implement a management program to reduce the potential for significant soybean yield loss,” he said.

First, he recommended applying a soil-residual herbicide at the full rate according to label guidelines for soil texture and organic matter no sooner than seven days before or no later than three days after planting.

Second, the initial post-application must be made when waterhemp is 3-5 inches tall.

Third, treated fields must be scouted seven days after the initial application to determine effectiveness. If waterhemp control is inadequate and retreatment is necessary, apply either a second application or a different product at the full labeled rate.

Fourth, re-scout treated fields within 10-14 days to determine effectiveness. “If scouting reveals plants treated with a second herbicide application might survive, implement whatever tactics are feasible to rogue these plants from the field before they reach a reproductive growth stage,” he said.

Hager said those tactics might include something as low-tech as hoeing or hand-pulling.

“New herbicide resistant traits are under development, but will not offer complete solutions,” Hager said.

He suggested an integrated management system should include herbicide/trait rotation, soil-residual herbicides and mechanical tactics.

“Switching traits and herbicides without integrating additional management tactics may not be enough. We have to consider what we can do to reduce introduction of seed back into soil seed bank,” Hager said.