Waterhemp

Amaranthus tuberculatus

Family: Amaranthaceae

Other Scientific Names:

Amaranthus rudis, Amaranthus tuberculatus var. rudis, Amaranthus tuberculatus var. prostrates, Amaranthus tuberculatus var. subnudus, Amaranthus latissimus, Amaranthus ambigens, Amaranthus cannabinus, Acnida altissima, Acnida cannabina, Acnida concatenata, Acnida subnuda, Acnida tamariscina, Acnida tuberculata, Montelia tamariscina

Other Common Names: rough-fruit waterhemp, roughfruited amaranth, tall waterhemp, common waterhemp
Weed class: A
Year Listed: 2026
Native to: Midwest and great lakes regions of the United States.
Is this Weed Toxic?:

livestock

Why Is It a Noxious Weed?

Waterhemp grows fast, has high seed production, and is drought tolerant. It is highly competitive in crop fields. Due to herbicide resistances, waterhemp is difficult to control once established.

How would I identify it?

General Description

Waterhemp is a summer annual, broadleaf herbaceous plant, which grows p to 3 meters in height, but can be much shorter.

Flower Description

Flowers are light green, inconspicuous, not showy, and grow in clusters on spikes at the tops of the plants or along the stems near where the leaves grow. Male and female flowers grow on separate plants. Male plants have softer flowering clusters, which have a lot of pollen when mature. Female plants' flower clusters are much more bristly to the touch.

Leaf description

Leaves are attached to the main stem by stalks, which grow alternately up the stem. Leaves can be egg, lance, or diamond shaped. They can grow to 4 inches long and over 1 inch wide.

Stem description

Stems usually branch, and are usually smooth. They can be green to red, and can have various patterns, such as lines going up the stalk.

Fruit Seed Description

Seeds are very tiny (about 1mm long), dark brown to black, and are very numerous.

May Be Confused With

Amaranths can be very difficult to id to species. Burke herbarium image collection of amaranths found in Washington.

A similar (in appearance and impacts) Class A weed, palmer amaranth (Amaranthus palmeri) leaves commonly exhibit a distinctive V-shaped variegation and prominent venation, differentiating it from other species. Leaves on waterhemp are often narrower than those on A. retroflexus (common ragweed), A. powellii, and A. hybridus. The pattern and amount of small hairs on stems and leaves of Amaranthus species may be able to help identify individuals, but this method of identification has not been formalized in the literature.

Where does it grow?

Despite growing well in wet and riparian areas, waterhemp is very drought tolerant and can also grow in dry and disturbed areas. It grows well in agricultural fields.

How Does it Reproduce?

Seed only.

How Do I Control It?

Cultural

Prevention is the best method!!!

Use known seed stocks, soil, and nutrients. Clean boots, tools, and vehicles between sites.

Crop rotations and increasing crop diversity can help outcompete waterhemp. Cover crops that don't allow light to reach waterhemp seedlings can also be effective. Narrow row spacing can help in a similar way.

Mechanical

Small infestations can be hand pulled. Make sure to get out the tap root, especially before the plant has flowered.

Manual

Tilling and cultivation can control newly emerged seedlings, especially if buried more than 1.4 inches below the soil. More mature plants can survive being buried or cut. Mowing will only cause waterhemp to flower closer to the ground.

Biological

There are no biological agents approved for waterhemp. Some options are being researched in Europe.

Chemical

Due to already acquired herbicide resistances, as well as quick development of herbicide resistances, it is recommended to rotate through herbicides with different modes of action each year, or even within a growing season. Pre-emergence and early post-emergence herbicides are the most effective.

Here is some information on control of waterhemp, including with herbicide, and herbicide resistances.