University specialists warn against new invasive weed

The first case of Palmer Amaranth was found last month in Yellow Medicine County

Melissa Steinken

University of Minnesota specialists want to boost awareness and save area crops after a fast-growing and dangerous pest was spotted in the state.

Palmer amaranth, known by farmers as Palmer Pigweed, was found in Minnesota’s Yellow Medicine County Sept. 22. The weed has been found in 28 other states, including Iowa, South Dakota and Wisconsin, where it damages row crops like corn and soybeans.

Tim Velde, a farmer in Yellow Medicine County, said it takes extraordinary effort to get rid of the pest.

“Hand weeding is about the only method of controlling it,” Velde said, “But believe it or not, spending the day walking up and down the field is good aerobic exercise but not a lot of fun.”

Palmer amaranth can grow two to three inches in a day and one female plant can spread 100,000 to 500,000 seeds.

To fight the weed’s early stages of growth in a new area, invasive plant specialists are encouraging farmers to find and eliminate the pest quickly, said Jeff Gunsolus, University of Minnesota Extension weed specialist.

Gunsolus said in order to eradicate the plant, farmers should burn it or mow the area, but this is unusual for most weeds.

While some farmers in Minnesota and Iowa control weeds by spraying glyphosate — a chemical found in Roundup pesticide — herbicides aren’t effective on Palmer amaranth.

“It is native to the U.S southwest and moved east and now it’s moving north,” said Bob Hartzler, Iowa State University Extension weed specialist. “I think it was inevitable that it was going to get here.”

Palmer Pigweed was first sighted in Iowa in 2013, Hartzler said. Farmers there were encouraged to plant more diverse species on their farms, but they unknowingly used seed mixes that carried invasive plants.

Even though it was surrounded by other plants that could have crowded it out, the Palmer amaranth survived long enough to threaten soybean and corn crops, Hartzler said. And to make matters worse, it’s extremely hard to identify.

“[The] unfortunate thing is, I estimate 95 percent of farmers or landowners don’t know they have a problem,” he said.

Palmer amaranth is not the only threat to crop productivity.

Waterhemp is a weed that has spent decades in agricultural fields and now poses a new threat because it looks so similar to Palmer amaranth.

“The problem with waterhemp and Palmer amaranth is they are the two weeds most efficient at evolving resistance to herbicides,” Hartzler said.

While farmers already use herbicides on weeds like waterhemp, Palmer amaranth is new enough to Minnesota soil systems that there is a chance it could be eliminated. The University of Minnesota’s Invasive Terrestrial Plants and Pests Center ranked Palmer amaranth the 20th most dangerous invasive plant species. Spotted knapweed was the greatest statewide threat.

On the list, Palmer amaranth ranked high in categories like proximity to Minnesota, impacts to yield and climate suitability.

“It’s a healthy debate, one that is ever changing because things are popping up,” said Heather Koop, MITPPC associate director. “When we wrote the report, Palmer amaranth hadn’t been here yet.”

Weed experts and researchers are trying to spread the word about the pest, but Hartzler said it can be difficult when most farmers don’t check the fields they plant.

Now, the weed is hard to locate because farmers rent out land and don’t walk the fields daily. When they do find Palmer amaranth, disposing it takes time and effort.

“It’s not fun, pleasant work,” Velde said. “It’s hard to find people to do it and not cheap to hire them.”