What is Palmer amaranth?
Palmer amaranth (Amaranthus palmeri) is a problematic annual broadleaf weed in the amaranth genus. It has several common names including carelessweed, dioecious amaranth, Palmer’s amaranth, Palmer amaranth and Palmer’s pigweed.
Palmer amaranth is native only to the Southwest and is considered a weed throughout the country. Field staff at the U.S. Department of Agriculture, Natural Resources Conservation Service, their partners, as well as farmers and landowners are working to eradicate these infestations before they spread to new areas.
Why the concern?
Palmer amaranth is a very fast growing weed that has spread out of native areas. Populations have developed resistance to multiple classes of herbicides with different modes of action, including glyphosate, making it very difficult and expensive to control, especially on productive farmland. It also is a highly competitive weed, and has been shown to be the most competitive of the pigweed species.
Palmer amaranth has an extended germination and emergence window, rapid growth rates and high water use efficiency, and it produces large quantities of seed. It is a very prolific seed producer, producing up to 250,000 seeds from one plant. Palmer amaranth has a fast growth rate of approximately 2─3 inches per day and commonly reaches heights of 6─8 feet, greatly inhibiting productive crop growth.
Yield losses have been reported up to 91% in corn and 79% in soybeans. The weed can also compete with and decrease other agricultural crop production. Palmer amaranth can also be toxic to livestock animals due to the presence of nitrates in the leaves.