Serving Montana Agriculture and growing prosperity under the Big Sky

Palmer Amaranth

(Amaranthus palmeri)

Palmer Amaranth detection image -spelled out


Palmer Amaranth

(restricted seed)

(Amaranthus palmeri)

Quick ID

  • Smooth, hairless stems
  • Petiole (leaf stalk) often longer than leaf blade
  • Dioecious, individual plants are either male or female
  • Seed heads on female plants are prickly and on both sexes are terminal and can be up to 3’ long, but can be shorter too
  • Leaves are diamond or oval-shaped
palmer amaranth location map
Figure 1. Surrounding states with Palmer amaranth in green. Larger image.
Palmer amaranth plant photo by Howard-F. Schwartz, Colorado State University,
Palmer Amaranth Plant

Video Information

Weed Images

Palmer Amar
Palmer Amaranth Seed - photo by Us Soybean Board
Palmer Amaranth Petiole - Photo by Bruce Ackley, The Ohio State University,
Palmer Amaranth Inflorescence - Photo by Joseph LaForest, University of Georgia,

Weed Specifications

Weed Info
Type Information
Toxicity Non-toxic
Best Management Practices

Prevention and early detection and rapid response, awareness, field scouting, equipment sanitation, communication, trusted seed source

*See additional documents below
Habitat Same as all pigweeds, mainly cropland and field edges, such as roadsides, fence lines, ditches, and other disturbed areas
Stem Reddish colored, smooth and hairless, and up to 8’ tall; other pigweeds in Montana, most predominantly redroot pigweed, have short, dense hairs and rarely exceed 3’ tall
Leaves Alternate, egg to diamond-shaped, the same length or shorter than the petiole, sometimes have a tiny hairlike tip
Lifespan Warm season annual, emerges throughout the growing season, not at specific times
Similar Looking Plants Redroot pigweed and other pigweeds, waterhemp
Important Information Produce hundreds of thousands of seeds per plant, plants can grow 2-3” per day and up to 8’ tall, can dramatically cut crop yields, resistant to multiple herbicide Modes of Action; spreads by seed, feed, mobile farm equipment, etc.; on Montana’s eastern border, it is found only two counties away; very hard to identify and expert assistance is necessary for confirmation, including being sent to a lab for genotyping

Become a Early Detection, Rapid Response Partner

Report the Weed

Find Out More...

To Report, Contact:



Dr. Tim Seipel
MSU Extension Cropland Weed Specialist
Palmer Amaranth Task Force Coordinator
Phone: (406) 994-4783