Pigweed, smooth

Image result for smooth pigweed

Images: (top) Smooth pigweed seedlings, VA Tech. (bottom) Mature smooth pigweed with seed heads, Missouri State University.

Smooth pigweed is a common summer annual weed in row crops. It is native and present throughout much of the US, with herbicide resistant populations confirmed in 12 states. Smooth pigweed looks very similar to redroot pigweed. All pigweeds are highly competitive with crops, are tolerate drought, and have high seed production. Distinguishing this pigweed from the more aggressive and multiple-resistant Palmer amaranth and waterhemp is necessary for proper management of herbicide resistant populations. Integrated weed management recommendations include:

  • Early and frequent scouting w/ proper ID
  • Cultivate young seedlings before and after cash crop planting
  • Apply effective herbicides to seedlings under 4 inches tall
  • Plant into weed-free soil
  • Plan crop rotations that vary the timing of tillage, planting, and other operations, as pigweed seeds germinate at various times in the season
  • Consider cover crops for preventing spring weed germination and creating a suppressive mulch
  • Select competitive cash crop varieties
  • Manage all plants before they are able to produce seed
  • Manually remove escaped weeds

Herbicide resistant populations:

  • Group 2
  • Group 5
  • Group 2 + 5

Locations of resistant populations:

Delaware, Illinois, Kentucky, Maryland, Michigan, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Virginia, Wisconsin


Pigweed Identification Manual: Redroot, Smooth, Palmer, and Waterhemp – Iowa State University

Scout and Identify Pigweed Species Now – Purdue University

Management of Triazine Resistant Pigweeds – an Integrated Approach – Penn State University