Leaving too much yield in the field

It did not take long after leaving a field day at the University of Missouri Bradford Research and Extension Center to find an on-farm example of Kevin Bradley’s latest talk.

Just two miles down the blacktop road was a field where it was hard to spot the soybeans through the weeds.

Weed escapes left untreated are limiting yield potential in many Missouri farm fields — not to mention affecting farm income.

“Farmers are leaving too much yield in the field,” the MU Extension weed specialist says. Bradley finds that for the most part, Missouri farmers are doing well with weed management in corn. “You guys have gotten after those early-season weeds that cause yield loss,” he told a group of farmers. “You are doing it right on corn, but we are not getting the same results with soybeans.”

His research showed that in 2011 there was an average 2.4-bushel-per-acre soybean loss because weeds were treated when they were either too big or too numerous.

“We need to do better from the standpoint of treating weeds in a timely manner.”

Persistent problem

For a number of years, preemergent herbicides have been the go-to treatment for weeds in soybeans. However, Bradley says there are many fields losing yields even with these treatments. He recommends spraying escapes.

Just how much yield loss from weed escapes depends on the species, density and size at spraying.

Not all weeds are created equal, Bradley warned. “Is having two waterhemp per square foot the same as two sunflowers? No.” He says farmers need to look at the competitive viability of weeds. Waterhemp is a yield-robber.

According to an in-state field survey, 87% of farmers said that waterhemp was their No. 1 weed. “And when it is 8 inches tall, that is way too big,” Bradley says. “You are not going to kill that size of waterhemp.”

Timing tips

He says that getting out early when weeds are early in their growth pattern offers the best suppression results. With a preemergent herbicide, Bradley says research shows that coming back and spraying two weeks later reduces waterhemp.

“You may be spraying on bare dirt,” he says, “but it works.”

Still some areas are just inundated with waterhemp. Bradley shares how sales of COBRA herbicide were higher this year than last. To him, that signals that farmers are really struggling to manage waterhemp.

“If you have waterhemp risks, I would strongly consider LibertyLink soybeans.”

Bradley says farmers have to change their management practices with escape weeds to get the most yields out of each field. “What we have been doing in weed control for soybeans is not working,” he says. “We have to be more diligent in eliminated escapes.”

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TALKING YIELD: Kevin Bradley, an MU weed scientist, visits with farmers about data that show that preemergent herbicides in soybeans may not be offering the best season-long control.

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INUNDATED: Weeds are taking over this soybean field in Boone County. Farmers need to spray these fields or face yield loss, according to MU researchers.

This article published in the September, 2012 edition of MISSOURI RURALIST.

All rights reserved. Copyright Farm Progress Cos. 2012.