Without proper management of waterhemp, especially during harvest season, the weed will continue to challenge farmers.

When patrolling fields this summer, Iowa farmers can expect to see one particular weed popping up.

Waterhemp has become a problem over the last decade, according to Bob Hartzler, an Iowa State University Extension weed specialist. Without proper management of the weed, especially during harvest season, waterhemp will continue to challenge farmers.

“In the majority of fields, (getting rid of) those escapes (from the fall) are not economic in the short term,” he said. “The problem is they are building up the seed bank. As that fills up, it makes it more difficult to achieve full-season control.”

Mike Koenigs, a market development specialist for Corteva AgriScience, said other weeds to look out for in 2019 across Iowa are giant ragweed, lambsquarter and morning glory. But he also stressed that waterhemp will be the main focus.

“That’s the weed we have to build our management systems around,” Koenigs said. “But with the delayed spring we are having and the wet, delayed fall, there wasn’t as much tillage or fall burndown done, so in addition to waterhemp, a lot of growers are seeing more weeds in their field.”

He said that tracking those straggler — possibly larger — winter annual weeds still present in fields is going to be key. To respond, it may require changes to the herbicide mix in the tank and being flexible if planters get out in the field before the sprayers.

“In some cases, we may need to increase rates because the weeds have increased in size,” Koenigs said. “In some cases we need to add additional tank mix partners to beef them up or broaden the portfolio of weeds they will control, to make sure everything gets taken down.”

While it has been a challenge for many farmers this spring, Koenigs said farmers need to make sure they stay with the right herbicides in their fields and do not forget the damage these weeds can do.

“We can’t forget the basics,” Koenigs said. “We can’t let grasses, waterhemp and giant ragweeds choke out that crop. The economics of corn production are very tight right now, but we can’t give up the basics. If we’ve done that, we’ve lost.”

Hartzler sad he understands the financial challenges for farmers at this time. Farmers are looking for ways to maximize their return on investment, which may mean using less herbicide. However, he continues to stress that farmers need to use full rates for long-term benefits.

“With the current economic scenario, farmers are looking for every place to cut costs, and unfortunately the herbicides are one of those,” Hartzler said. “We know you can reduce rates and still get effective control, but when we do that, it just hastens the speed resistance will evolve.”

Hartzler said the importance of pre-emergence herbicides is even more prominent as weed resistance evolves. He suggested using layered resistance, combining two pre- and postemergence products to achieve full-season control.

“Most growers are realizing that they really need to focus on the pre-emergence products,” Hartzler said. “We got in the habit of using the pre-emergence products to set us up for the postemergence application. As waterhemp is evolving resistance to all the postemergence products, I think people realize we need to use those pre-emergence products as the first line of defense.”