Weed of the month: Palmer amaranth

  • Palmer amaranthCommon name: Palmer pigweed
  • Scientific name: Amaranthus palmeri
  • Grass or broadleaf: Annual broadleaf
  • Commonly observed late spring through fall months and continues to emerge throughout the growing season — growing up to 3 inches per day in ideal conditions.
  • Known as the most competitive and aggressive pigweed species, Palmer amaranth can lead to corn yield loss up to 91 percent when allowed to compete with the crop throughout the growing season.1
  • Not only a threat to corn, season-long competition by Palmer amaranth at 2.5 plants per foot of row can reduce soybean yield by as much as 79 percent.1
  • Native to the Southwestern desert regions of the United States, devastation from Palmer amaranth has expanded across the Southeast and, recently, to the upper Midwest.
  • This invasive species has become one of the most significant weeds impacting cotton, corn and soybean production.

Fast facts from Jeff Ellis, Ph.D., field scientist, Dow AgroSciences

  • Palmer amaranth can adapt and quickly produce resistance genes to single-mode-of-action herbicides because individual plants are either male or female. This forces outcrossing and genetic diversity.
  • A single female plant can produce 600,000 seeds, which are rapidly spread through grain, seed, feed or equipment contamination.
  • Identifiable by its unique leaf shape, which is wide and ovate- to diamond-shape; Palmer amaranth leaves are commonly 2 to 8 inches long and a half-inch to 2½ inches wide.
  • Sometimes, the plants may show a white V-shaped watermark on the leaves. This watermark rules out other members of the pigweed family.

A fact that may surprise you …

  • Just how did an invasive desert plant make its way to the Midwest? Researchers believe Palmer amaranth was introduced to northern Indiana through manure from cattle that consumed seed-contaminated feed stocks from the South, such as cottonseed hulls. Farm equipment and wildlife also contribute to the spread of Palmer amaranth seed.

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 necessarily include all weeds in a population are resistant. Levels of resistance may vary in different areas of each state.

Tips for controlling and managing Palmer amaranth:

  • The key to mitigating Palmer amaranth is making control a priority before the weed emerges and addressing it when the plant is small. Given the threat Palmer amaranth poses to yield, growers should implement a season-long management plan, using residual herbicides with multiple modes of action to prevent Palmer amaranth seeds from spreading.
  • Tank-mix residual herbicides with postemergence herbicides to help avoid emergence issues later in the season. Layering residual products is important to control this weed, which germinates throughout the growing season.
  • Soybean farmers, especially, should always use residual herbicides to help control Palmer amaranth after crop emergence because there are few effective postemergence herbicide control options.

Tips for managing herbicide-resistant weeds:

Farmers in the Midwest and Midsouth are no strangers to some of the toughest weed species, such as: Palmer amaranth, waterhemp, ragweed and marestail. Implement these management best practices to help manage weed resistance issues during the season.

  • Develop an integrated weed management plan that delivers multiple modes of action throughout the season. The Enlist weed control system allows use of effective postemergence modes of action, including new 2,4-D choline, glyphosate and glufosinate in soybeans and new 2,4-D choline and glyphosate in corn.
  • Use full rates of the herbicides during applications. Do not use partial rates for any reason, including cost.
  • Spray when weeds are small. Although application can be challenging because of weather and other factors, timing is critical to achieve the best control.
  • Scout fields regularly to identify weeds when they are small and easy to control.

Dow AgroSciences weed control solutions:

Corn
SureStart® II herbicide
Resicore® herbicide
Keystone® NXT herbicide
Keystone® LA NXT herbicide 

FulTime® NXT herbicide
Surpass® NXT herbicide 
Durango® DMA® herbicide
Duramax® herbicide
Enlist Duo® herbicide, as part of the Enlist weed control system
Enlist One herbicide, as part of the Enlist weed control system

Soybean
Sonic® herbicide
Surveil® herbicide
Durango® DMA® herbicide
Duramax® herbicide
Enlist Duo® herbicide, as part of the Enlist weed control system
Enlist One herbicide, as part of the Enlist weed control system

Additional information:

Find more information using these weed science resources:
Palmer Amaranth In Minnesota — Minnesota Department of Agriculture
Palmer Amaranth Biology, Identification and Management — Purdue University Extension
Guidelines for the Identification and Management of Palmer Amaranth in Illinois Agronomic Crops — University of Illinois Department of Crop Science
Palmer Amaranth Identified in Nine Iowa Counties — Iowa State University Extension and Outreach/Integrated Crop Management

Sources:

1 Minnesota Department of Agriculture. 2017. Palmer Amaranth In Minnesota.
https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/palmeramaranth/palmeramaranthfs.aspx

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. FulTime NXT, Keystone LA NXT and Keystone NXT are federally Restricted Use Pesticides. Duramax, Durango DMA, FulTime NXT, Keystone LA NXT, Keystone NXT, Resicore, Sonic, SureStart II, Surpass NXT and Surveil are not registered for sale or use in all states. FulTime NXT, Keystone LA NXT, Keystone NXT, Resicore, SureStart II and Surpass NXT 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. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use in Enlist crops. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Always read and follow label directions. ©2017 Dow AgroSciences LLC