Flowering plant, Lee County, Iowa

Redroot pigweed in cornfield, Jefferson County, Iowa





Redroot Pigweed
(Amaranthus retroflexus,AMARE)

U.S. Distribution: Continental U.S.

Line drawings of plant features

: Seed leaves are long and narrow. First true leaves are strongly egg-shaped with a deep notch at the tip. As seedlings mature the stem becomes very roughly hairy.

Adults: Redroot pigweeds are tall plants with few branches. Stems tend to be green or reddish in color with green leaves. Stems and leaves are very hairy. Leaves are egg-shaped. Seedhead branches are few and tend to be short and stout with a prickly appearance.

Technical Characters
Bracts long, 4-7 mm. Tepals 5, longer than the fruit; apices obtuse or retuse, sometimes reflexed. Stigmas 3.

Redroot pigweed is less difficult in general to manage than common waterhemp. However, caution is needed. Some populations have triazine resistant biotypes. Although not currently resistant to ALS inhibiting herbicides, redroot pigweeds are known to hybridize with common waterhemp in Iowa. Although most hybrid individuals are sterile, they can produce some viable seed. These second generation hybrids have the potential to backcross resistance genes into redroot pigweed populations. An integrated program combining cultivation and appropriate herbicides should facilitate effective redroot pigweed control.