Weed of the Month: Waterhemp

waterhempWaterhemp is a competitive weed in the pigweed (Amaranthus) family, along with Palmer amaranth, redroot pigweed, and other pigweed species. Read the latest news on waterhemp and find weed management information from Dow AgroSciences field scientist Scott Ditmarsen.

Fast facts:

  • Common waterhemp is a slender, willowy plant with many branches. Mature plants range from 4 to 12 feet in height.
  • The species can be identified by its brightly colored leaves, varying from deep red or pink to emerald green. Its stems, leaves and seed head all may be differently colored on a single individual plant. Stems and leaves are very smooth and hairless, with a bright, glossy appearance. Leaves are long and narrow.
  • Its small seeds can only emerge from shallow depths, placing no-till fields at greater risk for waterhemp infestation.3

Resistance Statistics:*

According to WeedScience.org:

  • Herbicide classes
  • Multiple resistance: two sites of action
    • ALS inhibitors (B/2) and Photosystem II inhibitors (C1/5)
    • ALS inhibitors (B/2) and PPO inhibitors (E/14)
    • ALS inhibitors (B/2) and EPSP synthase inhibitors (G/9)
  • Multiple resistance: three sites of actions
    • ALS inhibitors (B/2), Photosystem II inhibitors (C1/5) and PPO inhibitors (E/14)
    • ALS inhibitors (B/2), PPO inhibitors (E/14) and EPSP synthase inhibitors (G/9)
    • ALS inhibitors (B/2), Photosystem II inhibitors (C1/5) and HPPD inhibitors (F2/27)

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

Weed management tips:

Scott Ditmarsen, field scientist, Dow AgroSciences, says:

  • Waterhemp is a very prolific seeder. It germinates throughout the growing season and is very competitive due primarily to its sheer numbers and rapid growth rate.
    • Although later-emerging waterhemp usually does not impact crop yield, it can produce a large amount of seed that can survive several years in the soil.
    • Waterhemp biotypes have also developed resistance to multiple (herbicide) modes of action, which presents additional challenges.
  • Identification of waterhemp can be difficult, especially at early growth stages, because it is a member of the pigweed (Amaranthus) family, along with Palmer amaranth, redroot pigweed and other pigweed species. These species tend to have similar characteristics. Consulting a weed identification guide can assist in properly identifying species in the field.
  • Appearance. Waterhemp cotyledons (seed leaves) usually are more egg-shaped than the longer and narrower cotyledons of other pigweed species, while the first true leaves of waterhemp typically are longer and more lance-shaped than those of other pigweeds. Also, waterhemp seedlings are hairless with shiny or waxy leaves; the stems are hairless, while other pigweed species have hairy stems.
  • Control. Timely and effective scouting throughout the growing season is required to identify waterhemp early to ensure timely herbicide applications and to identify potential problem fields for the following year.
    • Aggressive tillage and a program approach involving soil-applied herbicides followed by postemergence herbicide applications using multiple, effective modes of action is the best strategy to control waterhemp.
    • Any cultural practices that improve crop competitiveness will improve the effectiveness of herbicide programs. Physical removal of escaped plants to reduce competition and seed production, when feasible, is also recommended.

Dow AgroSciences weed control solutions:


SureStart® II herbicide
Keystone® NXT herbicide
Keystone® LA NXT herbicide

FulTime® NXT herbicide
Surpass® NXT herbicide 
Durango® DMA® herbicide
Duramax® herbicide
Enlist Duo herbicide


Sonic® herbicide
Surveil® herbicide 
Durango® DMA® herbicide
Duramax® herbicide
Enlist Duo herbicide 

Additional information:

More information can be found through these weed science resources:

1Everman, W., C. Sprague, S. Grower, and R. Richardson. 2010. An IPM Pocket Guide for Weed Identification in Field Crops.
2University of Illinois Extension. 2008. Recommendations for Management of Glyphosate-Resistant Waterhemp in Illinois Soybean. http://weeds.cropsci.illinois.edu/extension/factsheets/whempsoy.pdf.
3Nordby, D., B. Hartzler, and K. Bradley. 2007. Biology and Management of Waterhemp. https://www.extension.purdue.edu/extmedia/bp/gwc-13.pdf.

®™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. Enlist Duo herbicide is not yet registered for use on Enlist cotton. Duramax, Durango DMA, Enlist Duo, FulTime NXT, Keystone LA NXT, Keystone NXT, Sonic, SureStart II, Surpass NXT and Surveil are not registered for sale or use in all states. FulTime NXT, Keystone LA NXT, Keystone NXT, 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. Always read and follow label directions. ©2015 Dow AgroSciences LLC