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(Amaranthus tuberculatus)


(Amaranthus tuberculatus)

Quick ID
  • Smooth, hairless (glabrous) stems
  • Petiole (leaf stalk) usually shorter than leaf blade
  • Dioecious, individual plants are either male or female
  • Seed heads on male and female plants are not spiny
  • Elongated leaves, longer than wide, appear smoother and glossier than other pigweeds
Figure 1. Counties in Montana where waterhemp has been found since 2020. Click here for larger image.


Waterhemp Plant

Video Information

Weed Images

Waterhemp Stem - Photo by Bruce Ackley The Ohio State University,
Waterhemp Leaf - Photo by Bruce Ackley The Ohio State University,
Waterhemp plant - Photo by Bruce Ackley The Ohio State University,
Waterhemp Seed - Photo by Bruce Ackley The Ohio State University,

Weed Specifications

Weed Info
Type Information
Toxicity Non-toxic
Best Management Practices

Prevention and early detection and rapid response are critical, awareness, field scouting, equipment sanitation, communication, trusted seed sources

*See management plan below

Habitat As with other pigweeds, mainly cropland and field edges, roadsides, fence lines, ditches, and disturbed areas
Root Taproot with secondary fibrous roots
Bracts No spiny bracts, like redroot pigweed also has no spiny bracts, while Palmer amaranth female plants do have spiny bracts
Leaves Lanceolate, long and narrow, longer than the petiole, shiny, upper leaves are smaller and more lanceolate than lower leaves, while other pigweeds have a more ovate (egg-shaped) leaf
Lifespan Annual, with a long germination period of 8-10 weeks
Similar Looking Plants Other pigweeds, including redroot pigweed and Palmer amaranth
Important Information Extremely competitive and quickly develops resistance (already has widespread resistance to multiple herbicide modes of action) due to being a prolific seed producer, with each plant averaging 250,000 seeds and able to produce up to a million seeds, being dioecious (having plants that are either male or female), allowing for mixing of genes and more diversity, and being a quick grower, with 1”-2” of growth per day not uncommon, and since postemergent herbicides are most effective on waterhemp when it is smaller than 4”, the rapid growth can lead to a short spray window;  female waterhemp plants can be distinguished from male plants because female plants have smaller flowers, are less branched, and they produce very small dark colored seeds, which can be seen when a mature seed head is rolled between the hands; waterhemp was confirmed in Roosevelt County in 2020 and Prairie County in 2021, the State Weed Coordinator and Montana State University specialist staff were informed, both samples were sent to the Schutter Diagnostic Lab by the county extension agents, and then to the National Agricultural Genotyping Center; be aware of seed sources and transportation corridors; 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