Weed of the Month: Palmer Amaranth

  • Palmer AmaranthCommon name: Palmer pigweed
  • Scientific name: Amaranthus palmeri 1
  • Grass or broadleaf: Annual broadleaf
  • Native to the Southwestern desert regions of the United States, Palmer amaranth has expanded rapidly across the Southeast and can be found in multiple Midwestern states.1
  • Germination timing: Palmer amaranth emergence is from early May until mid-September. This long emergence period forces farmers to manage the weed throughout the year, unlike other summer annual weeds that are typically managed only through early summer.1
  • Competitiveness: Known as the most competitive and aggressive pigweed species, Palmer amaranth can lead to soybean yield loss up to 79 percent and corn yield loss up to 91 percent in some states. It also can significantly increase production costs.2
  • Palmer amaranth grows fast – as much as 2 to 3 inches per day – and commonly reaches 6 to 8 feet.2
  • Farm equipment, specifically combines, and wildlife can spread Palmer amaranth seed into new, previously uninfected fields.1

Fast facts

  • Palmer amaranth has dioecious reproduction, meaning plants are either male or female, which forces outcrossing and genetic diversity.1 This makes it more difficult to control.
  • Each plant can produce 100,000 or more seeds when it competes with a crop. In noncompetitive scenarios, each plant can produce nearly a half million seeds.
  • According to WeedScience.org, the first confirmation of glyphosate-resistant Palmer amaranth in Midwest corn, cotton and soybean fields occurred in Missouri in 2008.
  • To identify Palmer amaranth, look for smooth green leaves arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond-shaped. There may be a small, sharp spine at the leaf tip.2
  • Palmer amaranth seeds are small and thrive in no-till or minimum-tillage fields.1

Weed management tips1

  • Rotate crops: this allows farmers to use herbicides with additional modes of action in the field.
  • Practice deep tillage: this will bury the small Palmer amaranth seed below its preferred emergence depth.
  • Plant a cereal rye cover crop: this crop can provide a mulch that will suppress Palmer amaranth emergence.
  • Harvest heavily infested fields last: because machinery so easily spreads Palmer amaranth seeds from one field to another, consider harvesting fields or parts of field with infestations last to limit seeds to that area.

Resistance Statistics*

  • According to WeedScience.org, herbicide-resistant Palmer amaranth has been documented in corn and soybean fields in 24 states: Alabama, Arkansas, California, Delaware, Florida, Georgia, Illinois, Kansas, Kentucky, Louisiana, Maryland, Michigan, Missouri, Nebraska, New Jersey, New Mexico, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, Virginia and Wisconsin.

*Resistance confirmation does not include all weeds and may vary among different areas of each state.

Corteva Agriscience, Agriculture Division of DowDuPont, offers the following weed control solutions:

Corn

DuPont Cinch® ATZ herbicide
Durango® DMA® herbicide
Elevore herbicide
Enlist Duo® herbicide, as part of the Enlist weed control system
Enlist One herbicide, as part of the Enlist weed control system
FulTime® NXT herbicide
Keystone® LA NXT herbicide
Keystone® NXT herbicide
DuPont Realm® Q herbicide
Resicore® herbicide
SureStart® II herbicide

Soybean

Durango® DMA® herbicide
Elevore herbicide
Enlist Duo® herbicide, as part of the Enlist weed control system
Enlist One herbicide, as part of the Enlist weed control system
DuPont EverpreX® herbicide
FirstRate® herbicide
Sonic® herbicide
Surveil® herbicide
DuPont Trivence® herbicide

Additional information:

For more information, read these weed science resources:

Sources:
1Purdue University Extension 2013. Palmer Amaranth Biology, Identification, and Management. https://www.extension.purdue.edu/extmedia/WS/WS-51-W.pdf
2Minnesota Department of Agriculture 2018. Palmer Amaranth in Minnesota. https://mda.state.mn.us/plants-insects/palmer-amaranth-minnesota

®™Trademark of The Dow Chemical Company (“Dow”) or E. I. du Pont de Nemours and Company (“DuPont”) or affiliated companies of Dow or DuPont. Cinch ATZ, FulTime NXT, Keystone LA NXT and Keystone NXT are federally Restricted Use Pesticides. Cinch ATZ, Durango DMA, Elevore, EverpreX, FulTime NXT, Keystone LA NXT, Keystone NXT, Realm, Resicore, Sonic, SureStart II, Surveil and Trivence are not registered for sale or use in all states. FulTime NXT, Keystone LA NXT, Keystone NXT, Resicore and SureStart II are not available for sale, distribution or use in Nassau and Suffolk counties in the state of New York. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Enlist Duo and Enlist One herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use in Enlist crops. Always read and follow label directions. ©2018 Dow AgroSciences LLC