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September 20, 2013

Palmer amaranth confirmed in Iowa: what does it mean for Minnesota?

ST. PAUL, Minn. (9/20/2013)—Palmer amaranth, an invasive weed that can bring about crop yield losses exceeding 90 percent, has been reported in western Iowa.

What does this mean for growers in Minnesota? Since this weed is not known to be present in Minnesota, rapid early detection and eradication before any permanent population can become established is key.

Remove suspect plants before they can produce seed; that will help prevent Palmer amaranth from becoming a long-term problem in Minnesota.

Palmer amaranth has been the bane of growers in the South for some time. In recent years, populations of Palmer amaranth have been found more to the north in Nebraska, Illinois, Wisconsin, Indiana, Ohio, Michigan, and now in Harrison County, Iowa, near the Missouri River. It's been called a weed-management "game changer" for several reasons:

  • It's competitive, with reported yield losses up to 78 percent in soybeans and 91 percent in corn.
  • It grows quickly - up to three inches a day.
  • It produces large amounts of seed.
  • It has the propensity to resist glyphosate and other classes of herbicides.

Although Palmer amaranth looks similar to waterhemp and other pigweed species, some key identifying characteristics include long leaf petioles (stalk that attaches the leaf to the stem) and a long, unbranched inflorescence (seed head) that is prickly to the touch.

This is a good time of year to identify Palmer amaranth. Purdue University released "Identifying Palmer Amaranth in the Field," a video to assist in identification:
Growers in Minnesota at greatest risk of a Palmer amaranth infestation include those that feed cottonseed meal or "gin trash" to their animals. Since Palmer amaranth is widespread in cotton-producing areas of the South, cotton-related feed sources could be contaminated with Palmer amaranth seed. Not all weed seeds are killed by the animal digestion process or by composting manure. Thus, viable Palmer amaranth seed can pass through animals fed cotton-related sources and be spread onto fields through a manure application.

Check fields with "waterhemp escapes" to rule out Palmer amaranth. If Palmer amaranth is suspected, remove plants from the field immediately to help prevent additional seeds to the weed seedbank.
Also, please contact us at the University of Minnesota Extension. Where Palmer amaranth is suspected or confirmed, weed management practices in following years will need to account for Palmer amaranth, as this weed has proven to be very challenging to manage.

Lizabeth Stahl, University of Minnesota Extension, 507-372-3900,

Any use of this article must include the byline or following credit line:
Lizabeth Stahl is an Extension Educator and Jeff Gunsolus is an Extension Agronomist in Weed Science with University of Minnesota Extension
Media Contacts: Allison Sandve, U of M Extension, 612-626-4077,; Catherine Dehdashti, U of M Extension, (612) 625-0237,
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