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Palmer Amaranth Now Confirmed in Five North Dakota Counties

This pigweed that originated in the desert can survive and thrive in Northern climates.

As if North Dakota farmers didn’t have enough bad news this year with soybean tariffs and an October snowfall, here’s another one. Palmer amaranth has now surfaced in five North Dakota counties.

The aggressive and hard-to-control pigweed family member first was found in a row-crop field in McIntosh County this summer. Since then, it’s been confirmed in Benson, Dickey, Foster, and Richland counties. Plants in two counties were confirmed through laboratory analysis, and North Dakota State University (NDSU) Extension specialists confirmed the plants as Palmer amaranth in the other two counties.

Palmer amaranth differed in the way it reached each county, says Tom Peters, North Dakota State University Extension sugar beet agronomist. Palmer amaranth seed was likely dispersed via:

  • Migratory birds.
  • A used combine.
  • An alternative out-of-state feed source.
  • Custom combining.
  • Grain cleaned out of railroad cars.

Contaminated seed, wildlife, water, and wind are among other ways Palmer amaranth seeds can spread. Other sources include:

  • Potting soil.
  • Hay from other states.
  • Native seed mixes used for pollinator or wildlife habitats.

Tough to Identify

Because Palmer amaranth resembles other pigweeds, it can be difficult to identify. Once someone contacts Extension about suspected Palmer amaranth, an Extension agent or specialist, or both, visit the field and investigate to determine what it is. If necessary, they also send samples to the University of Illinois Plant Clinic for DNA testing. Lab results take about two weeks. Here's how producers, landowners, and others can learn more about Palmer amaranth and how to spot it through a website developed by NDSU Extension. 

One way to distinguish it from other pigweeds is its leaf stem, or petiole. Palmer amaranth’s petiole is as long as or longer than the leaf blade. Another clue is the female plant has spiny bracts that are bristly to the touch in the leaf axils and seed head. The seed heads can grow up to 2 feet long.

Anyone who sees a plant that may be Palmer amaranth should contact a local NDSU Extension agent as soon as possible.

1 Million Seeds

Palmer amaranth poses a serious threat to crops in North Dakota and other states because it can grow 2 to 3 inches per day in optimal conditions and reach a height of 6 to 8 feet. A single plant can produce up to 1 million seeds. Especially heavy infestations have reduced yield up to 79% in soybeans and 91% in corn in other states. Unlike other annual weeds that need to be controlled only through early summer, Palmer amaranth emerges throughout the growing season.

Palmer amaranth also is a huge challenge to growers because it is prone to herbicide resistance.

The weed originated in the desert region of the southwestern U.S. (New Mexico and Arizona) and northern Mexico. After that, it spread to the Mississippi Delta before invading other states, including Missouri, Kansas, Iowa, Wisconsin, Minnesota, and South Dakota.

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