Minnesota: Check Fields for Palmer Pigweed This Fall

Flowering palmer pigweed. Note how the leafstalk (petiole) is longer than the leaf blade on lower leaves. Photo: Minnesota Department of Agriculture

Flowering palmer pigweed. Note how the leafstalk (petiole) is longer than the leaf blade on lower leaves. Photo: Minnesota Department of Agriculture

The fall harvest season is a good time to look for the presence of Palmer amaranth. Palmer amaranth is on Minnesota’s prohibited noxious weed and seed list with the goal to eradicate Palmer amaranth before it becomes widely established.



Palmer amaranth is on Minnesota’s prohibited noxious weed and seed list with the goal to eradicate Palmer amaranth before it becomes widely established.

To date, the Minnesota Department of Agriculture (MDA) has been able to eradicate Palmer amaranth in the fields reported to them and will continue to monitor affected fields and track down sources of contamination.

The key is proper identification and rapid reporting to the MDA via the Arrest the Pest line at 1-888-545-6684 or arrest.the.pest@state.mn.us

Identification is key

Although Palmer amaranth can be confused with other amaranth (pigweed) species throughout the growing season, the fall is generally when Palmer amaranth literally stands out from the other pigweeds.

In a field that was cut or mowed earlier in the season, look for rapid regrowth. In the fall, Palmer amaranth can reach 5 to 6 feet tall, terminating in a 2 to 3 foot long seed head. The bracts that surround the many seeds on the seed head are pointed and sharp when touched.

The pollen producing male seed heads will be equally as long but lacking the bristly bracts. Petioles that attach the leaf to the main stem of the plant are generally longer than the length of the leaf itself.

Palmer amaranth has long flowering spikes that are spiny. The plant can produce hundreds of thousands of seeds in a short time frame. Seeds mature within 10-12 days after pollination. Photo: MDA
Close-up of female Palmer amaranth plant found in Yellow Medicine County. Note the spiny bracts. Photo: Bruce Potter.

To see additional photos of amaranth species, visit here.

Status of Palmer amaranth in Minnesota

To remain current on Palmer amaranth status please go here.



At this site, you will find the nine counties reported to the MDA where an affected field resides. When you click on a county you will see the name of the county, the contamination source (if known), land use, date of last detection and treatment, total number of sites and acres infested and current weed population status.

Sites contaminated with Palmer amaranth are monitored by the MDA for up to three years.

Sources of contamination

The contamination source of the four counties reported in 2017 were from native seed mixtures and Palmer amaranth is no longer present. Two of the three counties reported in 2018 were due to contaminated manure and the other source remains unknown.

One of the two 2019 sites was due to a contaminated proso-millet seed lot used in a prevent field and the other site in Houston County remains unknown. For more details on the newly detected site in Houston County, please read the MDA’s recent press release.

You can help



Prompt reporting not only assists the MDA in preventing the rapid spread of Palmer amaranth, but it helps to identify the source of the contamination so that proper screening and educational programs can be rapidly put in place.

For example, manure has been recently identified as a pathway of introduction for Palmer amaranth. This has opened up a new group of stakeholders that need to be made aware of the threat of Palmer amaranth to crop production.

To date the reporting model that is in place has been a very effective eradication model with the farmer, crop consultant, MDA and University of Minnesota working in a cooperative and efficient manner. Thank you for your cooperation and stay alert.

Source URL: https://blog-crop-news.extension.umn.edu/2019/09/check-your-fields-this-fall-for.html