Palmer Amaranth Found In Redwood County

Palmer Amaranth Found In Redwood County

MDA investigating the source of the plant, planning eradication efforts

St. Paul, MN: The Minnesota Department of Agriculture (MDA), in collaboration with University of Minnesota Extension, has confirmed a new Palmer amaranth infestation in a soybean field in Redwood County.

In mid-September, a farmer noticed several weeds he suspected as Palmer amaranth – a highly invasive weed. Genetic testing of four plants found in the field confirmed they were Palmer. MDA staff have scouted fields within a five mile radius of the soybean field and have not found any other plants. The MDA is investigating where the Palmer amaranth seed came from.

“Given the limited number of plants, we are optimistic this infestation is contained to a small area,” said 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 plant was found in Todd and Douglas counties. Because of eradication efforts at those sites, no Palmer amaranth has been 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 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 below ground 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 southwestern United States and northwestern Mexico. It has been found in over half of the states, including Iowa, North Dakota, South Dakota, and Wisconsin.


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In September 2016, Palmer amaranth, Amaranthus palmeri, was found in Minnesota. To date, it has been documented in Douglas, Lyon, Todd, and Yellow Medicine Counties. The Minnesota Department of Agriculture (MDA), University of Minnesota Extension, USDA, landowners and other partners are working to eradicate these infestations before they can spread to new areas.  

Why the concern?

Palmer amaranth is a fast growing weed native to the southwestern United States and northwestern Mexico, and has spread east and north. It has developed resistance to multiple classes of herbicides and their different modes of action, making it very difficult and expensive to control. Palmer amaranth is a prolific seed producer. Up to 500,000 seeds can come from one plant. It is also highly competitive.

It has a fast growth rate of 2- 3 inches per day and commonly reaches heights of 6- 8 feet, greatly inhibiting crop growth. Reported yield losses have been up to 91% in corn and 79% in soybean in some states. The weed can also significantly increase production costs for corn, soybean, and other crops.

What is the weed's legal status in Minnesota?

Since 2014, Palmer amaranth has been listed on Minnesota’s Prohibited Noxious Weed Eradicate List. All above and below ground parts of the plant must be destroyed. Additionally, no transportation, propagation, or sale of this plant is allowed. Failure to comply may result in enforcement action by the county or local municipality. More info on noxious weeds can be found on the MDA website.

In November 2016, the Commissioner of Agriculture listed Palmer amaranth as a Prohibited Weed Seed in agricultural, vegetable, flower, tree, shrub, native grass, and forb seeds sold in Minnesota. Any seed lot contaminated with Palmer amaranth is not legal for sale in Minnesota. To properly label a seed lot, the noxious exam must include genetic testing to determine whether any Amaranthus seed found may be identified as Palmer amaranth. Visit the MDA's Seed Program website for more information on seed regulations in Minnesota.

What can you do?

Be proactive and prevent Palmer amaranth establishment.  Familiarize yourself with Palmer amaranth identification and actively look for it in crop fields, borders, ditches, conservation lands and around dairies.

If you suspect Palmer amaranth on your property, immediately call your local U of M Extension Educator or IPM Specialist, crop consultant and/or the MDA’s Arrest the Pest (888-545-6684) to report locations.

AVOID entering areas where Palmer is suspected or confirmed.   If you must enter an infested area, always clean vehicles, equipment, and clothing prior to exiting.

If planting grasses and other flower mixes for conservation plantings, carefully review the seed label to ensure that no noxious weeds are present. If you are concerned, contact the Seed Regulatory Program at the MDA at 651-201-6531 for label review and sampling. Reputable seed sources will also be able to supply seed testing results for their seed mixes. 

How can you identify Palmer amaranth?

  • Palmer amaranth is a summer annual that commonly reaches heights of 6- 8 feet but, can reach 10 feet or more.
  • The green leaves are smooth and arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond or triangle shaped. 
  • The leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.
  • There are separate male and female plants.
  • Palmer amaranth looks similar to our native pigweeds such as tall waterhemp (A.  tuberculatus), Powell's amaranth (A. powellii) and redroot and smooth pigweeds (A. retroflexus and A. hybridus respectively). Here are some distinguishing characteristics:
    • Redroot and smooth pigweeds have fine hairs on their stems and leaves. Palmer amaranth and waterhemp do not have these hairs.
    • The petiole (stalk connecting a leaf to the stem) is longer than the length of the leaf. For tall waterhemp, the petiole will be only half the length of the leaf.
    • Seedhead spikes on female Palmer amaranth plants are much taller (up to 3 feet long) and more prickly than waterhemp or redroot and smooth pigweed spikes.
    • Genetic tests are available to confirm visual confirmation. Contact the MDA for labs offering this service.