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Dangerous Weed Invades North Dakota

Palmer amaranth has been discovered in North Dakota. Considered to be the "most troublesome weed in the USA," this may be a serious weed threat to farmers and gardeners in our state. Get to know this weed and how to control it in gardens.

Palmer amaranth
Palmer amaranth towers above a field of soybeans. Its stalks are massive and can damage equipment. This weed can be identified by its long petioles (note the petiole has been folded and is much longer than the leaf blade) and a spine on each leaf tip.

A very aggressive weed has been discovered in North Dakota. Palmer amaranth was detected in a farmer’s field in McIntosh County.

The Weed Science Society of America voted Palmer amaranth as the most troublesome weed in the USA. Retired NDSU Extension Weed Specialist Rich Zollinger claims Palmer amaranth is the most serious weed threat that farmers in North Dakota have ever faced. 

Why is everyone worried?

Adapts Quickly to Stresses. Each Palmer amaranth plant has either male or female flowers; but not both. This forces each plant to cross with a different plant and prevents inbreeding. This genetic diversity allows it to adapt quickly to different climates and stresses.

For example, one herbicide-resistant male plant can spread its pollen to female plants throughout the field, increasing levels of herbicide resistance in millions of their seeds. 

This desert weed from Mexico has adapted to the climates of the Mississippi Delta and Upper Midwest. It has developed resistance to Roundup and many herbicides.

Grows Aggressively. It grows up to 3 inches a day and 8 feet tall. The plants can overwhelm crops and damage farm equipment. The seeds germinate all summer and pieces of cut plants as small as 1 inch may resprout.

Produces Many Seeds. Each female can produce 100,000 or more seeds.

What does it look like?

It is a relative of redroot pigweed, waterhemp and love lies bleeding. It can be distinguished by its leaf petiole, which is long as or longer than its leaf blade. Its leaves have spines on their tips (see photos).

Will we ever see Palmer amaranth in our gardens?

It’s possible. The tiny seeds are readily spread by birds, wind, manure and equipment. Seeds may contaminate bird seed mixes, potting soil and hay.

How do we control it?

The same way we control other weeds in the garden: a sharp hoe. Kill the weed before it goes to seed. Pick up the cut weeds since they can resprout.

Palmer amaranth resists the most commonly used herbicides used in gardens: trifluralin (Preen) and glyphosate (Roundup). Deep plowing and the use of cover crops can help. Frost will kill the plants in fall.

Contact your local NDSU Extension agent if you ever see it. More information is available at https://www.ag.ndsu.edu/palmeramaranth/.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. 

Legleiter, T. and B. Johnson. 2013. Palmer amaranth biology, identification, and management. Purdue University Extension Publication WS-51.
Monsanto Company. 2018. Palmer amaranth–A weed to watch. Accessed online.
North Dakota State University. 2018. Palmer amaranth. Accessed online.
Sosnoskie, L.M., T.M. Webster, A.S. Culpepper and J. Kichler. 2014. The biology and ecology of Palmer amaranth: Implications for control. University of Georgia Extension Circular 1000.

Photos were made available under Creative Commons licenses specified by the photographers. Ross Recker, University of Wisconsin-Madison (2); Rebekah D. Wallace, University of Georgia, Bugwood.org; North Dakota State University. The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by North Dakota Extension is implied.

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