Stutsman County Extension Agent Alicia Harstad with a Palmer amaranth plant. Photo courtesy of NDSU Extension.

Weed scientist Brian Jenks with NDSU Extension is warning farmers about a noxious weed possibly heading their way.

A farmer discovered Palmer Amaranth — a rapidly-spreading pigweed — in McIntosh County in August 2018. It’s been found in nearly 30 states including Minnesota, Iowa and South Dakota

Jenks said it’s imperative that farmers take this weed seriously. Weed scientists are calling Palmer Amaranth, “America’s No. 1 weed enemy.”

“It’s unique because of how aggressive it grows,” Jenks said. “It can grow 2-3 inches per day and get 6-8 feet tall. We found Palmer last year that was easily 8 feet tall.

“And it’s a prolific seed producer. It can produce a million seeds per plant. This is why we want zero tolerance.”

In parts of Nebraska, it can cover fields quickly. Greg Krueger, with University of Nebraska-Lincoln Extension, said the weed itself isn’t new, but lately it has come with a new twist.

“We’ve had Palmer documented here for over 100 years, and we never thought of it as a major problem until it became glyphosate-resistant,” he said. “It completely changes things. Once it’s resistant, it’s a nightmare to deal with.”

Emergence

According to the USDA, Palmer is native to the desert southwest and northern Mexico. However, it has since made its way to the Midwest.

It’s been found in five North Dakota counties to this point – McIntosh, Dickey, Richland, Foster and Benson. As troublesome as that is, Jenks said a saving grace is that those counties are in eastern North Dakota, and that means there is a better chance of eradication.

If it’s found in western North Dakota, Jenks said it’ll be hard to control it.

“It would certainly thrive there,” Jenks said.

Stopping Palmer from entering North Dakota could prove to be difficult, though, as there are numerous ways for the weed to get here. 

Among the ways scientists believe Palmer has moved throughout the Midwest include sunflower screenings as animal feed, custom combining, manure spreading, migration of birds and hay donation. The latter is a big deal in that ranchers brought in hay from other states during a drought in 2017, especially to western North Dakota. If a drought occurs again and hay is transported from a surrounding state, Jenks said, “we need to be concerned about Palmer being in that hay.”

Jenks said farmers in other states have obtained manure from a feedlot for their fields, and “now they’ve got Palmer in their fields.” A University of Missouri study on Palmer found that 25 percent of the seeds were still viable after passing through the system of migratory birds, while the Palmer found in Benson County actually came from a rail car along the tracks.

“Somebody must have cleaned out railroad cars and Palmer was in that material,” Jenks said. “It makes you wonder how many cars have been cleaned out along the railroad tracks. It’s certainly something we need to keep an eye on.”

Eradication

If a farmer or rancher comes across Palmer Amaranth, Jenks said positively identifying it is the first step. Most types of pigweed typically have fine hairs on the main stem, but Palmer and water hemp do not. From there, Jenks said to look at the leaves coming off the main stem. If the leaf stem, or petiole, is longer than the leaf itself, then it’s likely Palmer.

Once it’s identified, Jenks recommends calling the local Extension agent so they can officially identify it before the farmer takes steps to remove it. Jenks said the farmer should be careful during removal.

“Bag it up, so we’re not spreading seeds all over the field,” he said. “We want to make sure we’re eradicating this plant as much as possible.”

Jenks said it’s important to recognize it early, as it’ll be difficult to contain if it drops seed — which can happen as early as July with a May emergence all the way until September.

“It emerges in all seasons,” Jenks said. “If it emerges in May, it’s probably not going to produce seeds till July or August. But if it emerges in August, it’s going to try and produce seeds as quickly as possible. The later it emerges, the quicker it tries to produce seeds. Last September, we saw Palmer that was 2 inches tall trying to put out a seed head. That’s one of the biggest reasons we need to be concerned.”

Krueger said farmers should have a plan if they find Palmer. Without a plan, serious yield loss could follow. The USDA reported it has seen losses of 91 percent in corn and 79 percent in soybeans.

“If you see Palmer Amaranth and you don’t manage it, you have three years,” Krueger said. “After three years, it’s over. The second year, it’ll come in patches, and the third year, it’ll take over your entire field. At that point, you might as well figure that you’re now growing Palmer Amaranth.”

Research

Ag research does its best to stay ahead of weeds, but it’s hard to compete with the efficiency, endurance and seed quantity of Palmer.

One of the benefits of Dicamba was to control Palmer and water hemp in soybean fields, but Palmer is fighting back, Jenks said.

“In Nebraska, they’ve already found some species resistant to Dicamba,” Jenks said. “Once it gets above 3 or 4 inches high, it can’t be controlled with post-emergence herbicides.”

Jenks said not every Palmer plant is resistant to glyphosate — some plants can be eradicated with herbicides, while others are resistant to nearly everything. However, he stressed that an attitude of “zero-tolerance” is best to avoid the headaches associated with the noxious weed.

“We haven’t tested every Palmer plant to see what it’s resistant to, but we’re telling farmers to just assume that it’s glyphosate-resistant,” Jenks said.

Research is still being done to attempt to make identification easier for farmers. The National Agricultural Genotyping Center worked with NDSU Extension’s weed scientists to develop a rapid DNA test that can tell producers in seven days if Palmer is growing in their fields.

Krueger said farmers need to be on the lookout for Palmer and not just in their own fields.

“Folks in North Dakota need to take this seriously,” Krueger said. “I would encourage them to be proactive. You can say it’s the neighbors’ problem. But if they see anything at all, they better be careful. If it’s not actively managed, they’ll be dealing with it, too.”

– Chris Aarhus, Editor