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Palmer Amaranth

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Palmer amaranth
Palmer amaranth in field- Photo by Howard F. Schwartz, Colorado State University
Scientific Name: 

Amaranthus palmeri S.Watson  (ITIS)

Common Name: 

Palmer amaranth, palmer pigweed, carelessweed

Native To: 

Southwestern U.S. (Ward et al. 2013)

Date of U.S. Introduction: 

First reported outside of its native range in Virginia in 1915, but was not a significant weed in the Southeast until the 1990s (Ward et al. 2013); glyphosate-resistant varieties first appeared in 2004 (Culpepper et al. 2006)

Means of Introduction: 

Most likely through the transport of contaminated seed; some recent infestations in the Midwest were caused by contaminated Conservation Reserve Program seeding mixes (Ward et al. 2013; Murphy et al. 2017)


One of the most economically important weeds of corn, cotton, and soybean; some populations are resistant to glyphosate and other herbicides (Ward et al. 2013)


USDA. ARS. Tellus.

Pigweed is a major challenge to our farmers and growers. It is extremely resilient and resistant to many herbicides, posing a significant threat to the agriculture industry. ARS scientists in Stoneville MS, along with collaborators from Clemson University, are researching the pigweed itself to find ways to mitigate this highly adaptable weed.

USDA. National Institute of Food and Agriculture.
Last summer, farmers in the Midwest got an unwelcome surprise after planting native seed on Conservation Reserve Program acres: Palmer amaranth (aka Palmer’s pigweed), an aggressive and hard-to-kill weed that is native to the Southern United States. Pat Tranel, molecular weed scientist at the University of Illinois, noted that growers who sell seeds are in jeopardy due to the spread of this noxious weed. “Unless they have a way to certify their product is Palmer-free, they can’t sell it,” Tranel said. Tranel and graduate student Brent Murphy developed a way around these issues. Their low-cost method can identify Palmer amaranth DNA from within a mixed sample without having to grow the plants. This project was made possible with support from NIFA.
USDA. Natural Resources Conservation Service.
An invasive species is on the move and may be headed for Montana. Palmer amaranth, a giant pigweed, is known to have spread to at least 28 states, including Minnesota and South Dakota, but has not yet been reported in Montana. To prevent its spread into Montana, landowners are encouraged to check their fields to ensure the invasive weed is not present. It was a known contaminant in Conservation Reserve Program (CRP) seed mixes but pollinator, wildlife habitat and cover crop plantings may also been contaminated. Producers with recent conservation plantings should check their fields to ensure this invasive weed is not present.

United States Department of Agriculture. USDA Climate Hubs.

Palmer amaranth (Amaranthus palmeri S. Watson) is an annual plant in the pigweed family (Amaranthaceae). It is native to the southwest United States/northern Mexico deserts and is currently increasing its range across the country. USDA NRCS, their partners, as well as farmers and landowners are working to eradicate these infestations before they spread to new areas. Midwest Climate Hub fellow, Dr. Erica Kistner-Thomas is getting a jump on how the distribution of Palmer amaranth will change from current to future climate conditions. Climate change is going to benefit this heat-tolerant weed by lengthening its growing season, boosting seed production and expanding its potential U.S. geographic range.

Distribution / Maps / Survey Status

University of Georgia. Center for Invasive Species and Ecosystem Health.
Provides state, county, point and GIS data. Maps can be downloaded and shared.


University of Georgia. Center for Invasive Species and Ecosystem Health.


Google. YouTube; Penn State Extension. Pesticide Education Program; Pennsylvania Department of Agriculture.

Google. YouTube; USDA. Agricultural Research Service.

Selected Resources

The section below contains highly relevant resources for this species, organized by source. Or, to display all related content view all resources for Palmer Amaranth.


European and Mediterranean Plant Protection Organization.

University of Georgia. Center for Invasive Species and Ecosystem Health.

North Central Integrated Pest Management Center.

See also: Pest Alerts for more resources

Michigan State University. Midwest Invasive Species Information Network.
Federal Government
USDA. Natural Resources Conservation Service.
See also: Technical Publications - Plant Fact Sheets for more resources
USDA. Natural Resources Conservation Service.
USDANRCS. National Plant Data Center.

USDAARS. National Genetic Resources Program. GRIN-Global.

State and Local Government
Minnesota Department of Agriculture.

University of Idaho Extension.

PNW 758 - A Pacific Northwest Extension Publication

University of Florida. Institute of Food and Agricultural Sciences Extension.

Electronic Data Information Source Publication #SS-AGR-336

Montana State University Extension.

University of Delaware. Cooperative Extension.

See also: Weed Management Guides for more resources

University of Maryland Extension.

See also: Invasive Plants for more resources

University of Illinois. Department of Crop Sciences. Weed Science.
Pennsylvania State University. Cooperative Extension.
New Mexico State University. College of Agricultural, Consumer and Environmental Sciences.

Iowa State University. Extension and Outreach. Integrated Crop Management.

University of Minnesota Extension.