Palmer Amaranth | Nebraska Invasive Species Council

Credit: Rebekah D. Wallace, University of Georgia, Bugwood.org

General Information

Species Name: Amaranthus palmeri

Also Known As: Palmer pigweed, carelessweed

Family: Amaranthaceae (Pigweed)

Growth Form: Forb

Life Span: Annual

Flowering Dates: July-October

Origin: Southwestern U.S.

Toxic: No

Noxious: No

Why Is It Invasive?

Palmer amaranth is especially invasive of crop fields and greatly reduces crop yield upon establishment. It is particularly damaging to annual crops and causes extensive damage to corn and soybean crops. Palmer amaranth is resistant to many popular herbicides, making it difficult to control.

What Does It Look Like?

General Characteristics

Palmer amaranth is a summer annual that can reach greater than 10 feet in height.

Flowers

Green, flowering spikes that mature to a brown color. Female plants have spiny, sharp bracts around each small flower part, causing flowering spikes to feel sharp or rough. Flowering spikes of male flowers are soft to the touch.

Leaves

Leaves are alternately arranged and egg-shaped or oval. They are smooth and have white veins on the underside. The stem that attaches the leaf to the main stem is the same length or longer than the leaf.

Stems

Stems are waxy, smooth, and reddish, sometimes with red stripes, They are upright and branching. Stems may appear ridged.

Seeds

Reddish-brown and glossy. Very small.

Photos

Green flowering plant with long, curved stems against a clear blue sky.

Credit: Howard F. Schwartz, Colorado State University, Bugwood.org

Green leafy plant with broad leaves growing in sunlight.

Credit: Joseph M. DiTomaso, University of California - Davis, Bugwood.org

Young plant with reddish stems and green leaves in a small pot; ruler visible in background.

Credit: Bruce Ackley, The Ohio State University, Bugwood.org

Five glossy brown seeds on a pale gray background, with a size reference in millimeters.

Credit: D. Walters and C. Southwick, Table Grape Weed Disseminule ID, USDA APHIS PPQ, Bugwood.org

Green weed with spiky seed clusters in a grassy field under a blue sky.

Credit: Rebekah D. Wallace, University of Georgia, Bugwood.org

Tall green weed with elongated flowering stems in a lush crop field.

Credit: Howard F. Schwartz, Colorado State University, Bugwood.org

Tall green palmer amaranth with spiky stems and leaves under a clear blue sky in a rural field setting.

Credit: Ross Recker, University of Wisconsin-Madison, Bugwood.org

Palmer amaranth with thin leaves on dry soil, farmland visible in the background.

Credit: Joseph M. DiTomaso, University of California - Davis, Bugwood.org

Where Does It Grow?

Palmer amaranth is native to southwestern United States and has begun spreading northeast. It can be found in crop fields, grasslands, roadsides, rangelands, and disturbed, sunny sites. It is very drought tolerant.

How Does It Spread?

Palmer amaranth reproduces via seed, with as many as one million seeds per plant that can remain viable for up to 5 years. Seeds can spread through natural vectors or human vectors, including plowing, harvesting, and attaching to clothing, pets, and equipment. It was initially reported outside of its native range in the early 1900s and was likely introduced in contaminated seed.

How Do I Control It?

Mechanical

Mowing can be done in conjunction with other methods, but will not effectively control palmer amaranth independently. Hand weeding can be effective but tedious. If hand weeding, ensure that you bag and dispose of the entire plant to prevent seed spread. Plants laid on soil can re-root and continue to grow.

Please contact your county weed control authority to determine appropriate removal methods.

Cultural

Rotate crops so that you can use a variety of herbicides on cropland. Consider planting a cereal rye cover crop, which can suppress palmer amaranth. When buying hay or forage, check to make sure it is weed-free certified.

One way that invasive plant seeds and fragments can spread is in soil. Sometimes plants are planted purposefully. You can prevent the spread of invasive plants.

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