Common waterhemp in cornfield. Wapello County,
(Amaranthus rudis, AMATA)
Texas to Ohio.
drawings of plant features
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.
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.
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).
Bracts short, 0.9-2.8 mm. Tepals 5, all midribs short, extending 0-0.6 mm
beyond the tepal blade apex.
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.