The super weed Palmer amaranth has been found in a seventh North Dakota county in a year's span and in south central North Dakota for a second time this summer.
DNA testing of a sample that a crop scout submitted to North Dakota State University Extension officials confirmed the presence of Palmer amaranth in Emmons County, the state Department of Agriculture said Wednesday, just a couple of weeks after announcing the discovery of the weed in Grant County, to the west of Emmons. Both discoveries were confirmed by the National Agricultural Genotyping Center in Fargo.
The aggressive pigweed species was first confirmed in North Dakota in August 2018, in soybeans in McIntosh County, which borders Emmons County on the east. It has now been confirmed either by NDSU Extension specialists or through laboratory analysis in the counties of McIntosh, Benson, Dickey, Foster, Richland, Grant and Emmons.
Palmer amaranth can grow as tall as 7 feet and produce hundreds of thousands of seeds. It's able to resist many herbicides, and it's strong enough to stop combines. A heavy Palmer amaranth infestation can cut soybean yields by as much as 79% and corn yields by up to 91%, according to research by Purdue University.
The weed discoveries in Grant and Emmons counties came in fields with millet, according to NDSU Weed Scientist Brian Jenks.
“I strongly encourage agricultural producers to monitor millet plantings for Palmer amaranth, as that may again be the likely source of infestation,” Agriculture Commissioner Doug Goehring said Wednesday. “With harvest season in full swing, farmers are encouraged to scout fields and clean excess dirt and plant debris off equipment between fields to prevent unintentional spread.”
The weed is native to the desert regions of the southwestern U.S. and northern Mexico and has been slowly spreading, moving into the Upper Midwest in recent years.
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NDSU Weed Science officials recognized the threat from Palmer amaranth by naming it the “weed of the year” in both 2014 and 2015, even though it hadn’t yet been found in the state. The North Dakota Department of Agriculture last January added it to the state's list of noxious weeds, which are required to be controlled under state law.
The recent discoveries in south central North Dakota don't necessarily indicate that the weed is becoming established in the state. It has been found this year in only two of the five counties in which it was confirmed last year, and "growers at these two locations are doing their best to prevent further spread and keep new plants from going to seed," Jenks said.
However, "I am much more concerned about what we’ve found in 2019 because Palmer density was much higher in the millet fields," he said.
"Assuming the Palmer came from contaminated millet seed, many more growers may have Palmer and don’t know it," Jenks said. "The plants are shorter because millet is planted later (June), but may be producing seed very soon, if not already."
State Noxious Weeds Specialist Richard Weisz said all of the documented Palmer amaranth in North Dakota most likely was introduced by nonnatural means, such as farm equipment or contaminated seed, and "diligent management is the key to controlling this weed."
More information on Palmer amaranth is available at https://www.nd.gov/ndda/plant-industries/noxious-weeds. To report a suspect plant, go to https://www.nd.gov/ndda/pa or contact a county weed officer or an NDSU Extension agent.