Palmer amaranth can rob up to 79 percent of soybean crop yields

Another weed threatens the crop fields of Minnesota’s soybean farmers — the Palmer amaranth.
“It’s a pretty big scourge for soybean plants. Palmer amaranth can rob a soybean yield of up to 79 percent,” said Joe Smentek, director of public affairs with the Minnesota Soybean Growers Association.
The Palmer amaranth prevents or slows down crop growth with its own rapid growth that can easily take out entire fields, if it is not dealt with promptly.
The plant doesn’t just affect soybeans. According to the USDA, up to 91 percent yield losses have been reported for corn. The plant can also be toxic to livestock animals, since the plant’s leaves contain nitrogen.
The Palmer amaranth is a summer annual member of the pigweed family, grows about 2-3 inches per day and reaches heights of 6-8 feet. Some can grow even taller, Smentek said.

Palmer amaranth is a fast-growing weed that can rob soybean crop yields by up to 79 percent.

In many ways, the Palmer amaranth looks similar to other pigweeds, such as the common water hemp, redroot and smooth pigweeds. But one difference is that while redroot and smooth pigweeds have fine hairs on their stems and leaves, the Palmer amaranth and water hemp do not, Smentek said.
One identifying characteristic that separates the Palmer amaranth from the common water hemp is the length of the stalk that connects a leaf to the stem. While the common water hemp stalk is half the length of the leaf, on the Palmer amaranth plant, the stalk is longer than the length of the leaf.
The leaves on the Palmer amaranth plant are smooth, oval to diamond-shaped and grows symmetrically around the stem. Some leaves may have a white V-mark, as well.
One distinguishing characteristic that contributes to the weed’s rapid spread across state borders is that one plant alone can produce up to 250,000 seeds.
“We have been watching it closely because of the damage it can do to soybean fields. We were very vigilant to not get it in Minnesota,” Smentek said.
However, the presence of Palmer amaranth was discovered last year in some conservation reserved areas in southwestern Minnesota
Smentek said the Palmer amaranth was found in the mix of flower seeds that were planted, but because of the United States Department of Agriculture’s (USDA) quick actions, the destructive weed was eradicated.
Because of the large damage the Palmer amaranth can do to the country’s crop fields, the USDA received extra funding this year to continue its fight against the weed, Smentek said.
Eradicating Palmer amaranth can be an expensive process in time and money. Since the weed is resistent to some glyphosate weed killers, such as Roundup, some farmers have had to hire people to help pull out the weeds by hand.
“Paying people and weeding manually can be expensive and time consuming,” Smentek said.
Even though the herbicide Dicamba is effective on Palmer amaranth, it can harm other soybean varieties that are not resistant to Dicamba, Smentek said.
“I’d rather have it so people do not have to spray anything. Prevention is the goal,” he said.
The Palmer amaranth seed often spreads from state to state through seed mixes. Since the weed is more prevalent in southern states, such as Iowa, Arkansas and Louisiana, Smentek recommends farmers get their seeds from approved vendors in Minnesota, North Dakota and South Dakota.
“Chances are higher that the seed is free from palmer amaranth then,” he said.
Another way to prevent Palmer amaranth is to actively scout the crop fields, borders, ditches, conservation lands and around dairies for it, Smentek said.
Smentek said the United Soybean Board’s Checkoff recommends farmers who find Palmer amaranth to bag the plant, pull it and then burn it. It is also recommended they contact the local extension agency or crop consultant about suspected or confirmed presence of Palmer amaranth.
The USDA also recommends that any vehicles, equipment or clothing that have come into contact with the weed be cleaned before exiting the infested area.