Source: Ohio State University and Purdue University  |   July 20, 2011 resize text

Ohio crop growers faced numerous challenges planting corn and soybeans this spring, and with the crop progressing through mid-July, they now face an interesting weed control scenario, as well.

"The late planting presents challenges and makes weed control easier at the same time," said Mark Loux, Ohio State Extension weed specialist. The unusual planting season resulted in an abnormal timeline for producers' weed control systems.

Because farmers couldn't get into fields as early as they would have liked to this spring, Loux said farmers saw significant weed pressure throughout June in both no-till and conventional tillage fields. In addition, some producers were not aggressive enough with their application of a burndown herbicide in no-till, and some weeds simply survived tillage this year.

Perhaps the biggest challenge to producers' weed control strategies boiled down to simple logistics.

"When we're planting that late, everyone gets jammed up and some missed applications," Loux said. "So, we have some fields that are really clean and some that are really messy."

In his travels around the state Loux said he was concerned that some producers had not yet sprayed a post-emergence herbicide. There is no point in waiting, he said, because establishing control of weeds as early as possible is critical in late planting situations.

Aside from the obvious challenges, a potentially shortened growing season does yield some positive impact on weed control.

"The good news in a late planting situation is you don't have as many weeks of weeds, and the crop grows faster," Loux said. "If you start weed-free and make that work, you can spray your post-emerge a little earlier and it makes control a little easier if you get the right start."

He continues to see glyphosate-resistant marestail as the key weed problem in the state, and 2011 may prove to be an enlightening year for some farmers because of the late planting.

While traditionally found in the southwestern portions of Ohio, Loux said resistant populations of marestail are now found throughout the state.

"We have a lot of marestail this season," he said. "We can't control it post-emergence very well. We have some problems in beans because farmers didn't pick the right combination of burndown herbicides, or they didn't want to spend enough money."

He also noted that in some cases, control efforts proved challenging because burndown application timing was much later than usual this season, and accordingly some products didn't work as well as in a typical year.

Since control efforts were hampered in some areas, Loux is hopeful affected producers will better understand how significantly their fields are infested with resistant weed populations and plan accordingly for next year.

"Because we have up to two types of resistance in some marestail populations, the biggest thing is to realize you have a problem," he said. "More of it is going to go to seed this year than last year. When you plan for next year, consider a fall application of herbicide, and be aggressive enough to control it next year."

The basic control recommendation in no-till soybeans, where Loux sees the most weed control issues, is to use a comprehensive spring burndown herbicide protocol while using the correct rate of a residual control product at the same time. Beyond that, farmers can modify a post-emergence application of glyphosate as needed.

He said some plans do include a fall application for marestail or other problem weeds, as well.

"For historically resistant fields, farmers can consider some Liberty Link soybeans to break up the use of glyphosate and get those issues under control," Loux advised. "Some farmers aren't willing to do that, though, because the variety selection there isn't as diverse."

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