A new Palmer amaranth infestation in a Redwood County, Minn., soybean field was recently confirmed by the Minnesota Department of Agriculture and University of Minnesota Extension.

In mid-September, a farmer noticed several weeds he suspected were Palmer amaranth — a highly invasive weed. Genetic testing of four plants found in the field confirmed they were Palmer.

MDA staff scouted fields within a 5-mile radius of the infected soybean field and did not find any other plants.

MDA is investigating the source of the Palmer amaranth seed.

“Given the limited number of plants, we are optimistic this infestation is contained to a small area,” says Mark Abrahamson, MDA’s director of plant protection. “Given its potential harm to our ag industry, we will search for a source of the plant and work with the farmer to monitor the area next year. We have successfully eradicated the plant in other parts of the state and will work to achieve the same results in Redwood County.”

Palmer amaranth was first discovered in Minnesota in 2016 in Lyon and Yellow Medicine counties. In 2017, the weed was found in Todd and Douglas counties. Because of eradication efforts at those sites, no Palmer amaranth has been found in the four counties in 2018.

Palmer amaranth can grow 2 to 3 inches a day, typically reaching 6 to 8 feet, or more, in height. Left uncontrolled, a single female Palmer amaranth plant typically produces 100,000 to 500,000 seeds. It is resistant to multiple herbicides, can cause substantial yield losses and can greatly increase weed management costs in soybeans and corn.

Because of the impacts it can have to Minnesota’s crops, Palmer amaranth is listed as a Prohibited Weed Seed. This means no Palmer amaranth seed is allowed in any seed offered for sale in the state.

It is also on Minnesota’s Prohibited Noxious Weed Eradicate List. All above- and belowground parts of the plant must be destroyed. Also, no transportation, propagation or sale of this plant is allowed.

The invasive weed is native to the southwest United States and northwestern Mexico. It has been found in over half of U.S. states, including Iowa, North Dakota, South Dakota and Wisconsin.

Source: Minnesota Department of Agriculture