Palmer amaranth found in Goodhue County

 Jared Goplen, Extension educator - crops

Long seed head of Palmer amaranth.
Photo: Lisa Behnken

The Minnesota Department of Agriculture (MDA) has confirmed Palmer amaranth for the first time in Goodhue County. The Palmer amaranth plants were found in two separate corn fields but the source of the infestation is currently unknown. As weed escapes become more obvious in row-crops, NOW is the time to be scouting for Palmer amaranth. Being observant now can prevent big headaches later on.

Identification characteristics of Palmer amaranth

Early detection and eradication of Palmer amaranth is key in reducing management costs and preventing the rapid spread of this difficult weed. Palmer amaranth is challenging to identify as many of the amaranth species (waterhemp, redroot pigweed, etc.) look similar. However, identification is easier as plants enter the reproductive phase of development, which is occurring now through September. For help in identification, please go to the following web link: http://z.umn.edu/palmerid.

Photo 1. Spiny bracts of female Palmer amaranth
plant.

Key characteristics to look for include:

1. Plant is smooth with no hairs on stems or leaves
2. Leaf petiole (the stalk connecting the leaf to the stem) is often longer than the leaf
3. Seed and pollen heads can reach 1 to 3 feet in length, which is longer than other amaranth species.
4. The most consistent characteristic is the spiny bracts found on the female seed head (Photo 1).

Sources of contamination

So far in Minnesota, confirmed contamination sources of Palmer amaranth have included: 1) native seed/pollinator planting mixtures, 2) contaminated manure (from contaminated sunflower screenings), and 3) contaminated cover crop seed. Several contamination sources where Palmer amaranth was confirmed are still unknown, but numerous other contamination sources exist. A list of common contamination sources includes:

1. Contaminated crop / cover crop seed (especially seed produced where Palmer amaranth is common)
2. Contaminated equipment
1. Used equipment recently purchased (especially from outside the region)
2. Custom farm equipment (especially custom combines)
3. Contaminated manure / feed ingredients
1. Sunflower screenings
2. Cottonseed
3. Purchased hay and straw
4. Any other byproduct feed ingredients produced where Palmer amaranth is more common
4. Wildlife
1. Migratory birds are capable of transporting Palmer amaranth and other weed seeds long distances.

Status of Palmer amaranth in Minnesota

An interactive map about the presence of Palmer amaranth throughout Minnesota, including sources of contamination and year of last detection can be found at: https://z.umn.edu/Palmer-amaranth-status-MN

Reporting Process

If you or your crop consultant suspect the presence of Palmer amaranth, the MDA and University of Minnesota Extension (U of MN) suggest the following reporting process:

1. Take pictures of the plant(s) in question before pulling them. Pictures should include clear visibility of the whole plant, a close-up of the leaf and where it attaches to the stem, the flower head, and a leaf with the petiole folded over.
2. Save plants in a refrigerated plastic bag for any genetic testing that may be needed.
3. Report the find to the Minnesota Department of Agriculture’s Arrest the Pest line at 1-888-545-6684 or arrest.the.pest@state.mn.us. UMN Extension Educators are available to assist in this process as well.

The key to successfully eradicating Palmer amaranth in Minnesota is early detection and reporting. Remember, you are not in trouble for having Palmer amaranth in your field, especially considering the numerous routes of entry. Plus, reporting means that you are not on your own when it comes to managing Palmer amaranth infestations. The MDA and U of MN Extension are working together with farmers and crop consultants to devise effective plans to manage Palmer amaranth infestations.

For more information

For more information regarding Palmer amaranth and its management, visit:
https://extension.umn.edu/annual-broadleaf-weeds/preventing-palmer-amaranth-minnesota