Common waterhemp in cornfield. Wapello County, Iowa


Seedlings


Female seedhead


Male flowers

Common Waterhemp
(Amaranthus rudis, AMATA)

U.S. Distribution: Texas to Ohio.

Line drawings of plant features

Descriptions
Seedlings
: Seed leaves are oar-shaped. First true leaves are lance-shaped with a slight notch at the tip. Seedlings are very smooth and the plants remain smooth.

Adults: Common waterhemps are slender and willowy plants with many branches. Plants vary greatly in size, from knee high to eight feet tall. Stems and leaves are often brightly colored, varying from deep red or pink to emerald green; stems, leaves, and seedhead all may be differently colored on a single individual. Stems and leaves are very smooth and hairless with a bright, glossy appearance. Leaves are long and narrow. Seedheads are long, slender and smooth. Male and female plants are found in approximately equal numbers.

Technical Characters
Pistillate flowers
: Bracts short, 0.5-2.5 mm. Tepals usually 1, but often absent. Stigmas 3. Fruit opening when mature, the seed falling free (dehiscent) or not (indehiscent).

Staminate flowers: Bracts short, 0.9-2.8 mm. Tepals 5, all midribs short, extending 0-0.6 mm beyond the tepal blade apex.

Management
Common waterhemp can be difficult to manage. Many biotypes are ALS herbicide resistant; there are also reports of triazine resistant biotypes. In addition, this species germinates later in the growing season and continues to germinate late in the growing season. Late germinating plants may only grow to a few inches but will flower and set viable seed. Narrow row soybean culture and rotary hoeing are not completely effective common waterhemp controls, but late cultivation, when row spacing is appropriate, or narrow row culture can minimize the impact of late emerging common waterhemp.