What to do about those winter annuals?
A weed might have the simple definition of being a plant out of place. But winter annual weeds can also be considered parasites. They take nutrients out of your soil. They remove moisture that may be needed for spring crop germination. They will clog up tillage equipment. But they do provide one benefit. They serve as the landing spot for moths to lay eggs that will turn into black cutworms. So they can’t be all bad. Right? Yeah, right. So how do you get rid of winter annuals, or should the question be, what should you not do in an attempt to control winter annuals?
There is a good chance your harvested fields are green, but maybe most of that are corn and soybean seedlings that have germinated after being victim to shatter loss from the combine header. No need to worry about those, since the frost will soon take care of that volunteer crop. However, they will soon be followed by such friends as common chickweed, henbit, and various mustard species, says University of Illinois weed specialist Aaron Hager. One of his recent newsletters indicates that early control is better than waiting until the onset of winter. The latter could turn out to be a waste of money.
Your first chore is to identify the types of weeds you have in your field, and then determine if a treatment is needed this fall. Some fields may be clean, but others may be lushly vegetated. And your weed crop may be a function of how much precipitation you have had recently. As you assess your problem, consider which herbicide you may want to use, but your favorite spring herbicide may not be a candidate for fall. For example, Hager says Atrazine is not labeled for fall application, which indicates you should check the label of the herbicide of choice.
Another consideration is the calendar, since Dual II Magnum is restricted to fall applications prior to October 31. It also has a temperature restriction, since it cannot be applied at more than 55º and the temperature must be falling.
As you move into late October and there has been sufficient time for winter annuals to emerge, their vegetative state could be sufficient for treatment with glyphosate or 2,4-D which have little soil activity. But if you want to apply an herbicide with more soil activity, then the earlier in October the better.
Hager says combinations of herbicides can also broaden your spectrum of weed control. That could be a combination of a contact herbicide plus an herbicide that has more soil residual activity.
The label of your herbicide may also restrict the geography for which it can be applied. Operations in the more southern reaches of the Cornbelt may be able to apply later in the season, since weed growth will be occurring later in the year, and begin again earlier the following year.
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