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Another Herbicide Issue: Spray Applied, Field Not Planted

Another Herbicide Issue: Spray Applied, Field Not Planted
Long rain delays raise issues about how long herbicides will stay around.

Two types of weed control dilemmas are first and foremost for corn growers right now. Some planted corn, especially in no-till, intending to spray alter. 'Later' has turned into weeks, and in some cases, corn has emerged. Yesterday's local news items dealt with what to do in that case. Obviously, weed control specialists say it's much easier if the corn is Roundup Ready or Liberty Link. Estimates are that about 80% of the corn planted this spring is Roundup Ready.

The same concept would apply for liberty Link corn where Ignite was to be applied as a post application. Ignite is the current formulation that contains the same active ingredient originally marketed as Liberty. Consult label instructions for how to proceed with Ignite on Liberty Link corn in this situation.

The second group of farmers who may be concerned about weed control chose to work ground and spray first, before planting. In some cases fields that were sprayed with pre-emergence herbicides and didn't get planted before it rained have been lying there for three weeks or more. If you applied herbicide especially early just to get the job done, the time since application may be even longer.

Several herbicide programs have been developed lately that involve putting down a residual herbicide early, then coming back with glyphosate in Roundup Ready corn or Ignite in Liberty Link corn, after weeds that came up later were emerged. In at least some cases, those soil-applied herbicides are designed to provide four to six weeks of control. If they were applied four to six weeks ago, the clock started running So if the corn is planted today or in the next few days you may run out of weed control  power before the four-to-six week window of product for young corn occurs. The result may be breakthroughs of weeds in the corn before you're intended to come back with the post application.

Late-emerging weeds get the break in springs like this. They include giant ragweed, shattercane, johnsonsgrass and other tough perennials including burcucumber. Scouting will be important so you can catch patches of weeds and take action later in the season before weeds get out of control.

Fortunately, if you applied residual, soil-applied herbicide several weeks go and haven't planted corn there yet, there's a relatively easy fix, says Mark Loux, weed control specialist at Ohio State University.

"You can throw down some additional residual herbicide now when you plant," Loux says. That means some extra expense, but it means you can still buy time before you will need to make a post-emergence application.

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