1. Minnesota Department of Agriculture
  2. Plants, Insects
  3. Plants
  4. Noxious & Invasive Weeds Program
  5. Palmer Amaranth
  • A hand holding a flower with a meadow in the background.
    A Palmer flower in a meadow.
  • A closeup of a Palmer flower with more Palmer plants in the background.
    Flowers are long and narrow, with tiny white flowers.
  • A field of soybeans with Palmer plants growing in the rows.
    Infestation in field of soybeans.
  • A field with only Palmer plants growing, and no crops are visible.
    Infestation in a row crop field.
  • Palmer plants have male and female flowers on separate plants.
    Male and female flowers side by side.
  • A closeup of a Palmer leaf with grass in the background.
    Palmer leaves have petioles longer than the length of the leaf.
  • A closeup of a leaf with a pointed tip and a white chevron marking.
    Leaves have a pointed tip and sometimes have a white chevron marking.
  • A group of green Palmer plants.
    Plants have leaves with very long petioles.
  • A seedling with bare ground in the background.
    A Palmer seedling. Palmer plants do not have hairs on the stems and leaves.
  • A seedling with white markings on the leaves.
    The leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.
  • An image of hundreds of Palmer seedlings.
    Palmer produces so much seed that seedlings carpet the soil.

Common Name: Palmer Amaranth
Alternate Names: Palmer pigweed, careless weed
Scientific Name: Amaranthus palmeri S. Watson
 

Legal Status

Prohibited Eradicate

All above and below ground parts of the plant must be destroyed. Additionally, no transportation, propagation, or sale of this plants is allowed. Failure to comply may result in an enforcement action by the county or local municipality.

Background

Palmer amaranth is an annual plant native to the arid southwestern United States and northwestern Mexico. It is a traditional food of Native Americans including the Navajo, Pima, Yuma and Mohave. Its life-cycle is adapted to desert conditions; it will germinate and grow to quickly produce abundant seed when water is available. Palmer amaranth was accidentally introduced to the southeastern US.

  • 1915 - First reported in Virginia but was not considered problematic for some time.
  • 1989 - Documented in a weed survey in South Carolina.
  • 1995 - Ranked the most troublesome weed in cotton in the Carolinas.
  • 2009 - Ranked the most troublesome weed in cotton in the southern US.

Palmer amaranth developed resistance to multiple classes of herbicides and their different modes of action making it challenging to control. Palmer amaranth seed was accidentally moved, perhaps with cotton meal, and continues to spread. It is causing extensive corn and soybean crop losses in many areas.

Learn more about Palmer amaranth in Minnesota.

Description

  • Palmer amaranth is a summer annual that commonly reaches heights of 6-8 feet but can reach 10 feet or more.
  • The green leaves are smooth and arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond-shaped. There is a small, sharp spine at the leaf tip.
  • The leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.
  • There are separate male and female plants.
  • Palmer amaranth looks similar to our native pigweeds such as tall waterhemp (A. tuberculatus), redroot and smooth pigweeds (A. retroflexus and A. hybridus respectively). Here are some distinguishing characteristics:
    • Redroot and smooth pigweeds have fine hairs on their stems and leaves. Palmer amaranth and waterhemp do not have these hairs.
    • The petiole (stalk connecting a leaf to the stem) is longer than the length of the leaf. For tall waterhemp, the petiole will be only half the length of the leaf.
    • Seedhead spikes on female Palmer amaranth plants are much taller (up to three feet long) and more prickly than waterhemp or redroot and smooth pigweed spikes.

Habitat

Palmer amaranth is adapted to the arid habitat of the desert southwest. Outside of its native range, Palmer amaranth has been documented in annual row crop fields and disturbed, sunny areas.

Means of spread and distribution

Seed is the means of spread and female plants are prolific seed producers. A study in Missouri documented more than 250,000 seeds produced per plant. Seed can be spread in water movement, by wildlife and via agricultural practices such as plowing, harvesting and spreading manure.

Palmer amaranth is documented in 28 states including neighboring South Dakota, Iowa and Wisconsin. It has been documented in Douglas, Lyon, Todd and Yellow Medicine Counties in Minnesota.

Impact

Palmer amaranth competes aggressively with crops. It has a fast growth rate of 2-3 inches per day and commonly reaches heights of 6-8 feet, greatly inhibiting crop growth. Yield losses have been up to 91% in corn and 79% in soybean.

Prevention and management

  • Be proactive and prevent Palmer amaranth establishment. Familiarize yourself with Palmer amaranth identification and actively look for it in crop fields, borders, ditches and around dairies. Palmer amaranth is difficult to control because it can be resistant to multiple classes of herbicides and their different modes of action. Populations of Palmer amaranth have been documented with resistance to one or more of the following classes: Dinitroanilines, triazines, ALS (acetolactate synthase) inhibitors, glyphosate and HPPD (4-hydroxyphenylpyruvate dioxygenase) inhibitor herbicide.
  • Mowing alone is not as effective as cultivation, as Palmer amaranth plants are usually not killed by mowing. They can regrow from cut stalks and set seed close to the ground. Mowing must therefore be done in conjunction with other methods of control like herbicide application, prescribed fire or propane weed torching to be effective.
  • Prevent all Palmer amaranth plants from producing seed if possible. Plants can be hand weeded and removed for disposal. If hand weeding is not feasible, contact your local University of Minnesota Extension agent, co-op, or certified landscape care expert for a specific herbicide recommendation.
  • Always clean vehicles and equipment after exiting infested areas. If seed was produced, deep tillage will reduce the quantity of seeds that can readily germinate.
  • A cereal rye cover crop can reduce Palmer amaranth germination and growth.

Toxicity

Palmer amaranth can be toxic to livestock if the concentration of nitrates in the leaves is high.

Forms + Resources
Online Map of Minnesota Palmer Amaranth Finds
Timeline of invasion and eradication of Palmer amaranth in Minnesota
External Links
Video: Identifying Palmer Amaranth in the Field
Minnesota Extension: Palmer Amaranth - a new weed to watch out for
Purdue Extension (pdf)
Iowa State University: Palmer Amaranth Identification (pdf)
Risk assessment
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