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Home > Plants, Pests & Pest Control > Pest Management > Noxious & Invasive Weed Program > NWAC > Risk Assessments > Palmer Amaranth

Palmer Amaranth Risk Assessment

Palmer amaranth plants, photo by University of Illinois
Palmer Amaranth, photo by University of Illinois

Latin Name: Amaranthus palmeri
Common Name: Palmer Amaranth

Reviewer: Roger Becker

Affiliation/Organization: University of Minnesota

Date: 8/08/2014
File #: MDARA00036PALM_8_08_2014

Final Results of Risk Assessment

Review Entity - Outcome

  • NWAC Listing Subcommittee - List as a Prohibited - Eradicate Noxious Weed
  • NWAC Full-group - List as Prohibited Eradicate
    Comments: Send to the Commissioner for an emergency 2015 listing.
  • MDA Commissioner - Approved 3/03/15 – Prohibited Noxious Weed – Eradicate List; Prohibited Noxious Weed – Eradicate List
Box Question Answer Outcome
1 Is the plant species or genotype non-native to Minnesota? Yes, non-native in Minnesota. Is native to the southern U.S. and Mexico; native to North America. Yes. Go to Box 3.
3 Is the plant species, or a related species, documented as being a problem elsewhere? Yes. Palmer amaranth is a severe problem in summer climates similar to Minnesota (see Hager 2013; Hartzler 2014a; and Legleiter and Johnson 2013). It has not been documented as a problem in states with winter climates similar to Minnesota, but it is anticipated it will do very well since it is an annual with a seedbank and seedlings that have performed well in states with freezing winter temperatures, and portions of the growing season in Minnesota are similar to locations further south where Palmer amaranth is a severe problem. Yes. Go to Box 6.
4 Is the plant species’ life history & growth requirements understood? Yes, documented in disparate articles, but oddly no classic biology of Palmer amaranth review article could be found. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
6 Does the plant species have the capacity to establish and survive in Minnesota?    
6A Is the plant, or a close relative, currently established in Minnesota? Yes. Palmer amaranth is not established in MN but a close relative, tall waterhemp, is. Tall waterhemp (Amaranthus tuberculatus (Moq.) Sauer), is common in Minnesota, and is similar to Palmer amaranth in that tall waterhemp is competitive, diecious, and resistant to several mode of action herbicide groups. Competitiveness of Palmer amaranth here is not known. We anticipate it would be very competitive similar to, or exceeding that of tall waterhemp (Bensch et al. 2003). Note: Amaranthus rudis and A. tuberculatus are now considered a single species, A. tuberculatus, common name, waterhemp (Pratt and Clark 2001). Yes. Go to Box 7
6B Has the plant become established in areas having a climate and growing conditions similar to those found in Minnesota? Palmer amaranth occurs at problematic levels in southern Indiana, Illinois, Missouri, and Nebraska. It has recently been found in South Dakota, in five locations in Iowa (Hartzler 2014b), and in one location in Wisconsin (Davis and Recker 2014). Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
7 Does the plant species have the potential to reproduce and spread in Minnesota?    
7A Does the plant reproduce by asexual/vegetative means? No. No. Go to Box 7C.
7C Does the plant produce large amounts of viable, cold-hardy seeds? Yes. Sexual, dioecious reproductive system. Produces up to 460,000 seeds per plant with competition, 1 million seeds per plant when grown without competition (Sosnoskie et al. 2014). Yes. Go to Box 7F.
7F Are sexual propagules – viable seeds – effectively dispersed to new areas? Yes. Palmer amaranth seeds are readily dispersed locally and over long distances, moved with farm equipment, feed stock, and livestock. It is rapidly dispersed across agricultural landscapes where it has become problematic. Dispersal has been documented in cotton meal used in livestock feed rations (Davis and Recker 2014). Yes. Go to Box 7I.
7G Can the species hybridize with native species (or other introduced species) and produce viable seed and fertile offspring in the absence of human intervention? Palmer amaranth has been shown to hybridize with tall water hemp (Franssen et al. 2001). Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
7I Do natural controls exist, species native to Minnesota, that are documented to effectively prevent the spread of the plant in question? No. No. Go to Box 8.
8 Does the plant species pose significant human or livestock concerns or has the potential to significantly harm agricultural production, native ecosystems, or managed landscapes?    
8A Does the plant have toxic qualities, or other detrimental qualities, that pose a significant risk to livestock, wildlife, or people? No, with one notable exception. Nitrate poisoning in livestock from consumption Amaranthus species or common lambsquarters has occurred when both of the following occur: a) conditions exist that promote excessive N accumulation and b) pigweeds comprise a significant portion of the forage available. For example, this has occurred in field corn where high levels of nitrogen fertilizer have been applied but the crop subsequently fails such as following hail, or in a drought where silage is harvested rather than taking the crop to yield grain. High percentages of the forage harvested are often pigweeds due to excessive growth due to low crop competition coupled with high nitrogen nutrient levels. No. Go to Box 8B.
8B Does, or could, the plant cause significant financial losses associated with decreased yields, reduced crop quality, or increased production costs? Yes. Up to 91 % yield loss in corn (Massinga and Currie 2002; Massinga et al, 2001) and 79 % in soybean (Bensch et al. 2003). Palmer amaranth is one of the most aggressive weeds in cropping systems in the south, southeast, and lower Midwest. It is threatening the ability to use conservation tillage (Price et al. 2001), is very competitive, is tolerant of shading (Jha et al. 2008), and has been shown to be allelopathic (Menges 1987 and 1988). Is not a host of arbuscular mycorrhizae fungi (Moyer-Henry et al. 2003). Yes. Go to Box 9.
9 Does the plant species have clearly defined benefits that outweigh associated negative impacts?    
9A Is the plant currently being used or produced and/or sold in Minnesota or native to Minnesota? No. No. Go to box 10.
10 Should the plant species be enforced as a noxious weed to prevent introduction &/or dispersal; designate as prohibited or restricted?    
10A Is the plant currently established in Minnesota? No. No. List as a prohibited/eradicate noxious weed.
10B Does the plant pose a serious human health threat? No. No. Go to 10C. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
10C Can the plant be reliably eradicated (entire plant) or controlled (top growth only to prevent pollen dispersal and seed production as appropriate) on a statewide basis using existing practices and available resources? Yes – List as a prohibited/eradicate noxious weed. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment..


Bensch, C.N., M.J. Horak, and D. Peterson. 2003. Inference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Sci. 51:37-43.

Davis, Vince and Ross Recker. 2014. Palmer amaranth identified through the late-season weed escape survey. Wisconsin Crop Weed Science. Accessed January 2014.

Franssen, A.S., Skinner, D.Z., Al-Khatib, K., Horak, M.J. and Kulakow, P.A. 2001. Interspecific hybridization and gene flow of ALS resistance in Amaranthus species. Weed science 49 (5): 598-606.

Hager, Aaron G. 2013. Guideline for the Identification and Management of Palmer Amaranth in Illinois Agronomic Crops. University of Illinois.

Hartzler, Bob. 2014a. Palmer amaranth: ID, biology and management. Iowa State University.
Hartzler, Bob. 2014b. Palmer amaranth in Iowa. Iowa State University.

Jha, Prashant, Norsworthy, Jason K., Riley, Melissa B., Bielenberg, Douglas G. and Bridges, William Jr. 2008. Acclimation of Palmer Amaranth (Amaranthus palmeri) to Shading. Weed science. 56 (5): 729-734.

Legleiter, Travis and Johnson, Bill. 2013. Palmer Amaranth Biology, Identification, and Management. Purdue Extension. WS-51.

Massinga, R.A. and Currie, R.S. 2002. Impact of Palmer amaranth (Amaranthus palmeri) on corn (Zea mays) grain yield and yield and quality of forage. Weed technology : a journal of the Weed Science Society of America. 16 (3): 532-536.

Massinga, R.A., Currie, R.S., Horak, M.J. and Boyer, J. Jr. 2001. Interference of Palmer amaranth in corn. Weed science 49 (2): 202-208.

Menges, R.M. 1987. Allelopathic effects of Palmer amaranth (Amaranthus palmeri) and other plant residues in soil. Weed science. 35 (3): 339-347.

Menges, R.M. 1988. Allelopathic effects of palmer amaranth (Amaranthus palmeri) on seedling growth. Weed science. 36 (3): 325-328.

Moyer-Henry, K.A., Burton, J.W., Israel, D.W. and Rufty, T.W. 2006. Nitrogen Transfer Between Plants: A 15N Natural Abundance Study with Crop and Weed Species. Plant and soil. 282 (1-2): 7-20.

Pratt, Donald B. and Clark, Lynn G. 2001. Amaranthus rudis and A. tuberculatus – one species or two? J Torrey Bot. Soc. 128 (3):282-296.

Price, Andrew J., Balkcom, Kip S., Duzy, Leah M. and Kelton, Jessica A. 2012. Herbicide and Cover Crop Residue Integration for Amaranthus Control in Conservation Agriculture Cotton and Implications for Resistance Management. Weed technology. 26 (3): 490-498.

Sosnoskie, Lynn M.,
Webster, Theodore M.,
Culpepper, A. Stanley, and Kichler, Jeremy. 2014. The Biology and Ecology of Palmer Amaranth: Implications for Control.

Additional references NOT cited in this risk assessment but of interest:

Cane, J.H., Buchmann, S.L. and LaBerge, W.E. 1992. The solitary bee Melissodes thelypodii thelypodii Cockerell (Hymenoptera: Anthophoridae) collects pollen from wind-pollinated Amaranthus palmeri Watson. Pan-Pacific Entomologist. 68 (2): 97-99.

Wikipedia contributors, "Amaranthus palmeri," Wikipedia, The Free Encyclopedia. Accessed July 22, 2014.

Kartesz, J.T., The Biota of North America Program (BONAP). 2013. Taxonomic Data Center. Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2013. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)]

USDA, NRCS. 2014. The PLANTS Database. 22 July 2014. National Plant Data Team, Greensboro, NC 27401-4901 USA. (Note: No EDDR maps shown. EDRR Maps does not show any U.S. data for Palmer amaranth).