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Plan Your Weed Control Strategy

February 23, 2010
By: Darrell Smith, Farm Journal Conservation and Machinery Editor

Devising a plan of attack to control winter annual weeds should be as top of mind as seed selection and nitrogen management. Don't wait until post-harvest and apply a herbicide or pull out the harrow as an afterthought.

"Experienced strip-till and no-till farmers know that the longer you go without tillage, the greater a problem winter annual weeds are likely to become—if they are not managed,” says Farm Journal Field Agronomist Ken Ferrie. "Those farmers have a control plan in place.”

Often, depending on location, that plan begins with a fall herbicide application, says University of Illinois Extension weed science specialist Aaron Hager. Strategies include applying a herbicide with residual soil activity before most of the winter annuals germinate; applying a nonresidual, burndown-type herbicide, such as glyphosate, 2,4-D or paraquat, to emerged weeds (including winter annual, biennial and perennial species) while they are still small; or a combination of the two.

"The goal is to reduce the amount of vegetation you have to deal with in the spring prior to planting, and possibly eliminate the need for a spring burndown herbicide application,” Hager says. "But remember that a burndown herbicide may still be needed before you plant.”

If your fall treatment program—tillage for conventional farmers or herbicides for no-tillers and strip-tillers—went according to plan, you're off to a good start. Unfortunately for many farmers, last fall was anything but according-to-plan; much tillage did not get completed and many fall herbicides did not get applied.

"Many areas have experienced two years of wet falls, followed by wet spring weather and late planting,”

Ferrie says. "If you were unable to do timely spring tillage and your winter annuals went to seed, the [weed] population is likely to take off.”

This past spring, many winter annuals did go to seed before they finally were controlled, Ferrie adds. Farmers had to till or plant through heavy mats of weeds, such as henbit and chickweed, and the weed seed bank in the soil was increased.

Effects of weeds. Uncontrolled winter annual weeds create many problems. "In no-till and strip-till, and to some extent in vertical tillage, a heavy mat of weeds keeps soil from drying out,” Ferrie says. "That leads to delayed planting—and planting into wet soil leads to sidewall compaction and open slots.”

Lush weed growth provides a habitat for seed corn maggots and cutworms. "You typically think of cutworms being a problem in no-till or strip-till because they have a lot of cover,”

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FEATURED IN: Farm Journal - Mid-February 2010

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