Weed Control Looms as Big Issue Due to Rain Delays

There are solutions, but management is crucial.

Tom Bechman

Published: May 24, 2010

Even in mid-to-late April, memories of the last two seasons were huge in farmer's minds. So when soil conditions were better than they had been in two to three seasons, they planted, even if it meant getting ahead of herbicide applications.

One farmer told us he was more worried about getting corn in the ground, then he would worry about weeds. Since you can usually spray a day or so before you can get back in to plant again, he figured he would get caught up when a shower stopped him from planting. That was good strategy, except for one thing. The shower turned into showers that stretched over two to three weeks.

"We're back to looking like the past two seasons as far as May goes," one northern Indiana farmer said recently. "We've got a good amount of crop planted- that's the difference. As far as working time in May, it's looking like last year.

Mark Loux, an Ohio State University weed specialist, recently related to Jennifer Stewart or Purdue University Ag Communications some options for farmers caught in that situation. The first question is what kind of corn is in the ground.

If corn is emerging and so are the weeds, "It's more critical for no-till farmers because the decision now becomes what to mix without damaging corn," he says. "Eighty percent of corn is Roundup Ready. So a grower can use glyphosate on small corn with 2-4,D and atrazine to control emerged weeds."

If your corn isn't glyphosate –tolerant or in the Liberty Link system, it's tougher. Growers need to ask tough questions to their dealers if they're in this boat, Loux says. What kind of mix will control what's out there that has emerged? What adjuvants can be used? Can it be applied on two-leaf corn? Five-leaf corn?

One problem that could arise is that if early post-emergence treatments are applied now, they may not provide adequate season-long control, especially for grasses, giant ragweed and water hemp, all weeds that tend to emerge late. They also won't control weeds usually controlled by preemergence herbicides, including shattercane, johnsongrass and burcucumber.

As a result, Loux suggests scouting later in the season, being ready to apply post-emerge herbicides if necessary.

If corn is up and you apply pre-emergent herbicides now as the early post-application, you may damage larger corn plants, Loux cautions. He also notes that if weeds get bigger than corn, they may already be suffering weed losses.