WSU Extension

Hortsense

Weeds : Redroot pigweed (Rough pigweed) : Amaranthus retroflexus
(revision date: 3/19/2019)

Family: Amaranthaceae
Cycle: Annual
Plant Type: Broadleaf

Use Integrated Pest Management (IPM) for successful weed management.

Biology
Redroot pigweed is a coarse, erect plant, growing two to three feet tall. The lower stems and branches and the upper portion of the taproot are frequently red or striped with red. Leaves are alternate, with long petioles and distinct veins. Branches or small flower clusters typically occur in the leaf axils. The majority of the flower clusters are at the top of the plant and appear as greenish, somewhat prickly, bushy-looking spikes. The small seeds are black and shiny. Redroot pigweed reproduces only via seeds, which can germinate any time conditions are favorable.
Habitat
Redroot pigweed is a common weed of gardens, cultivated areas, and waste places. Rarely, pigweed can become a lawn weed, where mowing will force it to lie close to the ground rather than growing upright. Redroot pigweed is widely distributed.

Management Options

Non-Chemical Management
  • Maintaining a healthy planting or turf area to provide competition will prevent weed establishment.
  • Cultivation (rototilling or hoeing) will effectively eliminate plants.
  • Hand-pull to eliminate weeds.
  • Mowing to prevent seed production is a very effective means of management. In lawns, mowing regularly at the proper height for the grass species may help minimize weed growth and invasion.
  • Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination.
Select non-chemical management options as your first choice!

Chemical Management

Apply according to label directions. Glyphosate products should be applied as spot treatments only! NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas
  • glyphosate
  • dichlobenil
  • oryzalin
  • trifluralin
  • products containing diquat
Turf areas
  • products containing 2,4-D
  • products containing MCPA
  • triclopyr
  • 2,4-D + MCPP + dicamba
Bare ground areas
  • glyphosate
  • oryzalin
  • products containing diquat
  • products containing 2,4-D
  • triclopyr
Images
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Caption: Redroot pigweed
Photo by: D.G. Swan
Caption: Redroot pigweed leaves
Photo by: R. Parker
Caption: Redroot pigweed flower spike
Photo by: J.A. Kropf
Caption: Redroot pigweed flowers
Photo by: D.G. Swan
Caption: Redroot pigweed seedling
Photo by: J.A. Kropf
Caption: Powell amaranth mature seedhead
Photo by: T. W. Miller
Caption: Redroot pigweed showing distinct veins
Photo by: T. W. Miller