With the Minnesota Department of Agriculture confirming the presence of Palmer amaranth in 30 plantings by 13 landowners in Yellow Medicine and Lyon counties, some farmers living miles away may figure this noxious weed isn’t in their fields so why become concerned about it.

“Anybody who plants row crops needs to learn about Palmer amaranth,” says Tony Cortilet, MDA’s noxious weed program coordinator. “Take time now to get on the internet, search for information and learn to identify it.”

Palmer amaranth, native in the southwestern United States and Mexico, has been traveling north for the past five decades. A prolific plant, Palmer amaranth can produce up to 500,000 seeds per plant, grow 2 to 3 inches per day and reach a height of 6 to 8 feet, and cause major yield losses — up to 91% in corn and 79% in soybeans, according to Minnesota scientists.

Palmer amaranth has been found in every Upper Midwest state except North Dakota, Cortilet says. It looks similar to our native pigweeds such as common waterhemp, redroot and smooth pigweeds.

Outbreaks have been caused by conservation seed mixes contaminated with Palmer amaranth seed. Most concerning is how fast the weed has taken hold in Iowa. Half the counties in that state have confirmed it, and an Iowa State University Extension weed scientist predicts it could be found across all of Iowa by year’s end.

So what could and should Minnesota farmers do?

Educating yourself is the first step, as Cortilet suggests. “We really want growers to understand the weed and to look for it,” he says. He says there are numerous resources available through MDA, the University of Minnesota Extension and crop consultants. “Growers are our best line of defense,” he adds. “Don’t get scared. Learn about it.”

Cortilet encourages growers to work with their crop consultants and to ask them to help scout for Palmer amaranth. If you find it, contact MDA or Extension.

When Palmer is next door
Bruce Potter, U-M Extension integrated pest management specialist based in Lamberton, suggests that farmers living in affected counties continue to use herbicide management tactics that are effective on waterhemp. Some good news, according to MDA and Extension, is that genetic tests done on Palmer weeds in southwest Minnesota show those weeds are not yet resistant to glyphosate and PPO inhibitor herbicide classes. Still, to control Palmer, scientists recommend full labeled rates of residual herbicides with multiple sites of action in corn and soybeans, crop rotations where possible, and postemergence herbicide applications when Palmer is less than 3 inches tall.

“Try to find any plants early to prevent seed production,” Potter says. “It will not be simple to identify this weed when small, but it can be done. Watch additional areas outside conservation plantings. Seed could have been moved by mowing equipment or other means before the infestations were discovered.”

Palmer has yet to arrive
For farmers who live beyond the thus-far affected areas, acknowledge that Palmer amaranth is one hardy traveler that knows how to move.

“There are several ways that seed might be transported to new areas, besides as a contaminant in conservation planting or other seed,” Potter says. “These include via farm equipment, railcars and other types of transportation from infested areas.”

Just because no one has spotted the weed in other areas of the state does not mean it is not there.

“We cannot be certain that the weed does not already exist in areas outside Yellow Medicine and Lyon Counties,” Potter adds. “As a result, all farmers should be looking for, and hopefully, reporting suspected infestations. Initial populations should be rogued to prevent seed production.”

If Palmer gets established in an area, expect it to be a long-term problem like other weeds, Potter says. “Fortunately, the seed is not extremely long-lived in the soil, so aggressive management in all rotational crops should be able keep populations in a field at a manageable level,” he says. On the other hand, poor management can lead to extreme weed control costs including herbicide, and mechanical methods including hand weeding.

Site specific plans
Since last fall, MDA has been working to control and eradicate Palmer amaranth. Cortilet says agency scientists and staff are working with the California Department of Agriculture and an independent lab to develop a DNA test for Palmer amaranth and to identify the seed in the 9-pound sample provided by the native seed company that was found to have sold contaminated seed to the farmers.

MDA also contracted last fall with the Minnesota Conservation Corp to spot-burn the five sites containing Palmer weeds.

Currently, MDA is working with U-M to develop site-specific eradication plans for areas found to have Palmer amaranth. According to U-M Extension, each site eradication plan will be unique and will require full time follow-up and attention. Each plan will provide details on traffic, people and equipment movement in the area; landowner education; multiyear seasonal scouting; herbicide application and monitoring; and burning and hand removal of weeds.

To learn more about Palmer amaranth, visit MDA's website, or watch a Purdue University Extension video about identifying Palmer.