Herbicide Recommendations for Noxious Pigweeds

Herbicide recommendations for management of noxious pigweeds in corn, soybean, and forages.
Herbicide Recommendations for Noxious Pigweeds - Articles


Joseph M. DiTomaso, University of California - Davis, Bugwood.org

General Guidelines:

It is important to learn about these two invasive pigweeds (Palmer amaranth and Waterhemp).

  • Know where they are prevalent across the country.
  • Know where they have been found in Pennsylvania.
  • Know the weed biology (aggressive germination, competitiveness, seed production, and herbicide resistance).
  • Know how they spread (equipment, feed, grain, hay, manure, mulch and seed).
  • Know how to reduce their impact including preventing their movement and spread.

Develop strategies to address Palmer amaranth and Waterhemp in Commerce.

  • Identify and address pathways for the movement and spread of these weeds.
  • Identify and address effective, consistent and complementary containment measures.
  • Collaborate with academia, government and industry to take effective preventative actions.

Herbicide recommendations:

Plant into a clean seedbed.

  • use tillage or an effective burndown herbicide for no-till

Always consider herbicide sites of action (SOA) or Group numbers.

  • Use tank mixes with different effect SOAs
  • Use multiple and effective SOAs and rotate with crops
  • Avoid using the same SOA each year

Use effective soil applied herbicides at planting.

  • Use Group 14 (PPO) in soybean followed by Group 27 (HPPD) in corn. Include Group 15 herbicides in the both corn and soybean.
  • Use full labeled rates

For postemergence treatments, make timely applications and apply to small pigweed (<4 inches tall).

  • Never apply glyphosate alone to emerged pigweed
  • Avoid the use of ALS type (Group 2) herbicides for pigweed control

Scout fields within 10 to 14 days after application.

These recommendations assume Group 9 (glyphosate) and Group 2 resistance (ALS-inhibitors).

1. General Burndown herbicides for Palmer amaranth and waterhemp.
Herbicide active
SOA (Group #)
dicamba (corn)
4Banvel, Clarity
atrazine (corn)
simazine (corn)
mesotrione (corn)27various


Consider planting Liberty Link soybean.

Plant into a clean seedbed.

  • Use tillage or an effective burndown herbicide for no-till

Use effective soil applied residual herbicides.

Effective preemergence herbicides are essential at or before planting.

  • sulfentrazone (Authority) or flumioxazin (Valor)-based herbicides
  • Use full labeled rates

Scout fields 10 to 14 days after application.

Apply timely early postemergence herbicide to small pigweed (<4 inches tall).

  • Reflex (1 pt) + glyphosate (or Liberty in Liberty Link soybeans)
  • Can add residual (group 15) to reduce need for another post herbicide (Dual, Warrant, Zidua/Anthem, Outlook)
2. Effective soil applied residual herbicides for soybeans.
Herbicide activeSOAProducts
flumioxazin14Valor products, Fierce, various
sulfentrazone14Authority products, Sonic, Broadaxe, various
saflufenacil14Sharpen, Verdict
metribuzin5Sencor, Glory, Tri-Cor
pyroxasulfone15Anthem, Fierce, Zidua
3. Effective Post soybean herbicides
Herbicide activeSOAProducts
acifluorfen14Ultra Blazer
fomesafen14Reflex, Flexstar


Best option: plant corn - many more choices for management.

Apply effective residual herbicide at or before planting.

  • Atrazine premix - good
  • Lexar, Corvus + atrazine - better

Scout field 10 to 14 days after application.

Apply post herbicide when pigweed is small (<4 inches tall).

  • Better to include herbicide with residual activity in addition to dicamba, glufosinate, or 2,4-D (Atrazine, Callisto (or other mesotrione product), metolachlor, acetochlor or Zidua/Anthem)
  • Avoid glyphosate or ALS inhibitors
4. Effective soil applied residual corn herbicides.
Herbicide activeSOAProducts
mesotrione27Callisto, Lumax, Lexar, Instigate, etc
isoxaflutole27Balance, Prefix, Prequel
acetochlor15Degree, Harness, Keystone
pyroxasulfone15Anthem, Zidua
5. Effective Post corn herbicides.
Herbicide activeSOAProducts
dicamba4Banvel, Clarity, Status
mesotrione27Callisto, Halex
tembotrione27Laudis, Capreno

Forages (alfalfa, grass hay/pastures)

Routine mowing will help reduce pigweed seed production.

  • However, pigweed stumps can regrow if not cut low enough

Alfalfa could be treated with Chateau or Prowl H2O plus Gramoxone between cuttings.

In grass hay or pastures, apply 2,4-D and/or dicamba or triclopyr-containing herbicides

6. Effective forage herbicides.
Herbicide activeSOAProducts
2,4-DB4Butyrac, various
dicamba4Banvel, Clarity, Status
triclopyr4Garion, component of Crossbow