FARGO - Palmer amaranth - voted the nation’s most troublesome weed by the Weed Science Society of America - has been confirmed in four more North Dakota counties, North Dakota State University said Friday.

The weed, identified for the first time in the state this summer in McIntosh County, now has been found in Benson, Dickey, Foster and Richland counties, too.

To encourage farmers to report suspect weeds, the identities of the producers with confirmed Palmer are not being released.

The weed reached the four counties in different ways, with likely sources being seeds carried by migratory birds, a used combine, feed purchased out of state, custom combining and grain cleared out of railroad cars, said NDSU Extension sugar beet agronomist Tom Peters, who has spearheaded Extension efforts to control and combat the weed.

Peters and others familiar with the weed have said that keeping Palmer out of North Dakota would be impossible. They’ve focused on identifying and controlling the weed through what they call a zero-tolerance policy to minimize its spread.

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Palmer amaranth, a huge and longstanding concern in the southeastern United States, is spreading into the Upper Midwest. The weed, which had been found in Minnesota and South Dakota before it was first reported in North Dakota, can damage farm equipment and devastate yields.

Yield losses of up to 91 percent in corn and 79 percent in soybeans have been reported.

The weed has a combination of traits that make it particularly dangerous and difficult to control:

  • It's a prolific seed producer, with a single plant producing as many as 1 million seeds.

    • The seeds are extremely small, making them relatively easy for farmers to spread unintentionally.

    • Seeds can lie dormant in the soil for years, waiting to germinate until growing conditions are favorable.

    • The seeds are unusually competitive with most crops, including corn and soybeans.

    • It can grow as much as 3 inches per day - and the bigger it is, the harder it is to control.

    • It’s prone to developing herbicide resistance.

    • It closely resembles other pigweeds, complicating identification even by experts. So DNA testing is sometimes needed to make certain.

To learn more about the weed and how to spot, visit this NDSU website: www.ag.ndsu.edu/palmeramaranth.