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Palmer amaranth coming

By Staff | May 29, 2014

PALMER AMARANTH is an aggressive noxious weed that has been confirmed in southwest Iowa and working its way north.

ANKENY (ISA) – Farmers still have a fighting chance to stop Palmer amaranth, a tough yield-robbing weed, from spreading in Iowa.

The Iowa Soybean Association and Iowa State University Extension are working together to provide information to keep the weed at bay.

Native to the southwestern United States, Palmer was first officially identified in Iowa in September 2013.

There’s now documented cases in the counties of Harrison, Page, Muscatine, Fremont and Davis.

Herbicide resistance, primarily to glyphosate, is an issue.

“We’re at a point that we can really restrict how quickly it spreads,” said Mike Owen, ISU weed specialist. “If we ignore it, in the next 10 years it could be infesting half the (row crop) acres in Iowa.”

That will decimate yields and the bottom line.

Experts say Palmer outbreaks in the South have caused complete crop failures. A mild to moderate infestation can result in soybean yield losses of up to 30 percent, with a potential revenue hit of more than $200 per acre.

Early identification and action within Iowa is paramount to mitigate the spread of Palmer, which resembles waterhemp.

“There’s increasing importance to know what weed species you have in order to figure out better prescriptive control methods,” said Dr. Ed Anderson, ISA senior director of supply and production systems.

ISU weed specialists are available to help identify Palmer amaranth, which is vital for appropriate planning.

Late May is the time to start scouting for Palmer, but it will germinate throughout the growing season.

Recommended control strategies for Palmer include soil-applied, residual herbicides and multiple effective modes of action.

Group 3, 15 and some group 14 products work well.

Post-emergent products are limited due to herbicide resistance, and should be used sparingly.

Cover crops and spot cultivation are also effective measures.

Waterhemp is a “relatively wimpy weed,” Owen said, and can be controlled with weaker herbicide doses unlike Palmer, which makes identification so important.

Contact Owen at (515) 294-5936 for management help.

For additional information, contact ISA’s Aaron Putze at (515) 334-1099.

For more take-action tips to manage Palmer amaranth, visit www.takeactiononweeds.com.

To learn more about ISA, go to www.iasoybeans.com.

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