Waterhemp

Waterhemp is a pigweed that grows quickly and produces up to 1 million seeds per plant. Herbicide resistant populations are many, and are prevalent throughout many US states. Some populations are resistant to 3-5 herbicide sites of action. This level and prevalence of herbicide resistant waterhemp makes it necessary to integrate multiple management practices in order to achieve optimal control. Integrated weed management recommendations include:

  • Prevent entry of new waterhemp seeds to the property by monitoring inputs and equipment for weed seed contamination
  • Prevent spread between fields by harvesting infested fields last, and cleaning equipment if it comes in contact with waterhemp
  • Apply herbicides when plants are under 4 inches tall for effective control
  • Include residual herbicides in tank mixes, as waterhemp germinates all season
  • Avoid reliance on herbicide sites of action with widespread waterhemp resistance
  • Cultivate young plants
  • Mowing will not kill most plants, and they will re-grow and produce seed. It should not be regarded as a full solution, but may help decrease seed-drop from escaped plants
  • Do not allow plants to produce seed. Remove and destroy 100% of plants before they mature
  • Read the resources below for further management recommendations.

Herbicide resistant populations:

  • Group 2
  • Group 4
  • Group 5
  • Group 9
  • Group 2 + 5
  • Group 2 + 9
  • Group 14
  • Group 9 + 14
  • Group 2 + 5 + 14
  • Group 2 + 9 + 14
  • Group 27
  • Group 2 + 5 + 27
  • Group 2 + 5 + 9 + 14
  • Group 2 + 5 + 9 + 27
  • Group 2 + 4 + 5 + 14 + 27

Locations of resistant populations:

Arkansas, Delaware, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Wisconsin

Resources:

Invasive Pigweeds: Palmer Amaranth and Waterhemp – Penn State

8 Key Points to Palmer Amaranth and Waterhemp Identification

Biology and Management of Waterhemp – Purdue University

Waterhemp Identification and Management in Corn and Soybeans – Michigan State University

Waterhemp Management in Soybeans – United Soybean Board

Management of Glyphosate Resistant Waterhemp in Corn and Soybeans – University of Missouri

The Good, the Bad, and the Ugly of Waterhemp Management – Successful Farming

Waterhemp Management: It’s System More Than Trait – Iowa State University

Herbicide Recommendations for Glyphosate-Resistant Waterhemp – Illinois Soybean Association

Synthetic Auxin Resistant Waterhemp