Flowering plant, Lee County, Iowa


Seedlings


Seedhead

Smooth Pigweed
(Amaranthus hybridus, AMACH)

U.S. Distribution: Eastern U.S.

Line drawings of plant features

Descriptions
Seedlings
: Seed leaves are long and narrow. First true leaves are strongly egg-shaped with a deep notch at the tip. Seedlings become hairy as they mature.

Adults: Smooth pigweeds are tall plants with few branches. Stems and leaves tend to be red or green. Leaves are egg-shaped. Stem and leaves tend to be slightly hairy, but not roughly hairy like redroot pigweed. Seedhead branches are numerous, long, thick, and slightly prickly.

Technical Characters
Bracts short, 3-5 mm long. Tepals 5, shorter than the fruit; apices acute to acuminate; straight. Stigmas 3.

Management
Smooth pigweed is less common than redroot pigweed in Iowa, and appears to be restricted to the southeastern corner of the state. Because it is extremely weedy in Illinois and Missouri, the potential for spread into Iowa from these states is great. Management of smooth pigweed is similar to that of redroot pigweed. Smooth pigweed biotypes outside of Iowa have been found with multiple resistances to ALS and triazine herbicides.