Weed control a 'hot' issue this season

Listen to RFD Radio's interview with Dr. Ford Baldwin on the growing problem of weed resistance.

Dan Grant

Published: Jul 2, 2012

The hot and dry conditions obviously haven’t been good for crop development so far this growing season.

But the extreme conditions apparently haven’t slowed weed growth at many locations. In fact, summer annual weeds in many soybean fields are nearly three feet tall, according to Aaron Hager, University of Illinois weed scientist.

“Plants that have escaped pre-plant tillage operations often have contorted, C-shaped stems as a result of being damaged by the field cultivator,” Hager said. “These plants can be very difficult to control with post-emergence herbicides.”

The most common weeds include horseweed/marestail, lambsquarters, and waterehemp. The large weeds in many fields may have escaped a pre-plant burndown application due to glyphosate resistance or the fact that environmental conditions before and during applications were not always conducive to good herbicide performance, Hager noted.

Glyphosate-resistant waterhemp can be controlled by PPO inhibitors or Liberty while cloransulam (FirstRate) or chlorimuron (Classic) can control glyphosate-resistant marestail in soybeans. However, control of marestail larger than 6 inches often is inconsistent, according to the weed scientist.

Control of large weeds this season may require some farmers to do it the old-fashioned way of manually digging the weeds up or cutting them down.

Such tactics have become more common in the Southern U.S. due to glyphosate resistance.

“We’ve essentially lost Roundup in the south as anything but a grass herbicide,” Ford Baldwin, weed scientist from Arkansas, told the RFD Radio Network last week at a Beck’s Hybrids field day.

Baldwin urged farmers in the Corn Belt to take proactive steps to limit the build-up of glyphosate-resistant weeds.
“You have opportunities up here we didn’t have, such as Liberty Link,” he told Midwestern farmers. “With corn rotation and soil-applied herbicides, you can start pushing this thing back.”

Baldwin also encouraged farmers to use rotation diversity and tillage diversity to help control weeds and slow the spread of glyphosate resistance.

“The days of easy weed control are gone,” he added.

Weed control will be among the topics discussed at the Southern Illinois University field day, which will be held July 12 at the Belleville Research Center. For more information about that event, contact Ronald Kruz at 618-566-4761.

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