|Palmer amaranth (Photo: University of Delaware Carvel REC, Flickr/Creative Commons)|
“It appears Palmer amaranth can evolve life-history traits that increase its potential to grow and reproduce in various cropping systems,” says Ramon Leon of the University of Florida, part of a research team that took samples of the weed from fields in Florida and Georgia with "widely divergent cropping histories – from short-statured vegetables and peanut crops to tall corn and cotton crops. The fields also varied in herbicide use. Some were devoted to organic production, while others had a history of intensive herbicide use." The research was published in Weed Science.
"Palmer amaranth is widely considered to be one of the most damaging and difficult to control agricultural weeds in North America, said a news release about the study. It tends to develop resistance to the weed killer glyphosate, sold mainly as Roundup, and has spread into the Upper Mississippi Valley. One of its common names is carelessweed, perhaps a warning that farmers should be diligent about removing it.
Michael Wines of The New York Times wrote in 2014, "Palmer amaranths seem as if they were designed by nature to outwit herbicides and farmers. Unlike many weeds, it has male and female versions, increasing genetic diversity — and the chances of a herbicide-resistant mutation — in each new seed. And each plant is astonishingly prolific, producing up to 200,000 seeds in an average field, said Dave Mortensen, a professor of weed and plant ecology at Pennsylvania State University." Mortensen told Wines, “If one out of millions or billions of seeds contains a unique trait that confers resistance to herbicide, it doesn’t take long when a plant is that fecund for it to become the dominant gene.”