Amaranthus palmeri

Species of plant

Amaranthus palmeri is a species of edible flowering plant in the amaranth genus. It has several common names, including carelessweed, dioecious amaranth, Palmer's amaranth, Palmer amaranth, and Palmer's pigweed. It is native to most of the southern half of North America. Populations in the eastern United States are probably naturalized. It has also been introduced to Europe, Australia, and other areas. The plant is fast growing and highly competitive.

The leaves, stems and seeds of Palmer amaranth, like those of other amaranths, are edible and highly nutritious. Palmer amaranth was once widely cultivated and eaten by Native Americans across North America, both for its abundant seeds and as a cooked or dried green vegetable. Palmer amaranth has a tendency to absorb excess soil nitrogen, and if grown in overly fertilized soils, it can contain excessive levels of nitrates, even for humans. Like spinach and many other leafy greens, amaranth leaves also contain oxalic acid, which can be harmful to individuals with kidney problems if consumed in excess. Because of its toxicity to livestock, As a result, the primary economic importance of Palmer amaranth to American farmers has been as a noxious weed and a competitor to more marketable crops, rather than as a crop in its own right.

In many places, the plant has developed resistance since at least 2006 to glyphosate, a widely used broad spectrum herbicide. Glyphosate resistant pigweed not only dominates in cotton fields, but also has wide ranging effects on other crops and productions. In 2014, the Texas Department of Agriculture asked the United States Environmental Protection Agency for permission to use the restricted chemical propazine on 3 million acres (1.2 million hectares) of cotton threatened by Palmer amaranth. The request was denied due to unacceptable risks to drinking water. In 2019, Kansas State University researchers documented a population of Palmer amaranth with resistance to 2,4 D and Dicamba in Kansas. Previously, Palmer amaranth in Kansas has developed resistance to ALS, atrazine, glyphosate and HPPD herbicides—mesotrione, Huskie, Laudis, Impact, and Armezon—leaving growers with very few postemergence options to manage this weed. An Arkansas population has developed fomesafen resistance. Gene drive technologies could provide a countermeasure: A gene drive agent could engineer A. palmeri to become glyphosate sensitive again. Such a wide ranging application of the technology should be carefully considered however.

Palmer amaranth may be the most aggressive pigweed species with respect to growth rate and competitive ability. Palmer amaranth in particular is highly competitive. It will outgrow cotton and is much more efficient. Growers of crops have not been able to provide adequate moisture to offset prolonged temperatures above with a heat index. In these conditions, many herbicides break down over time and Palmer amaranth will keep growing. It can grow from in three days, or less.

Pollen is most commonly spread by wind. In 2015, Palmer amaranth was chosen as "weed of the year" for the second year in a row as a "proactive approach to prevent Palmer amaranth establishment in North Dakota." As alien, this species was first found in South Africa in March 2018 with further records in different regions of the country as well as in northern Botswana in March 2020. It is considered as naturalized weed which invades both ruderal and segetal (growing in cornfields) plant communities.