Aggressive weed that threatens crops spreads

It can grow as much as 3 inches per day and as tall as 7 feet, with each plant producing hundreds of thousands of seeds.

BISMARCK, N.D. —A weed that’s strong enough to stop combines and resist many herbicides has been found in North Dakota for the first time, the state Agriculture Department said in July.

A farmer has found Palmer amaranth in a soybean field in McIntosh County, in the state’s southeast. The finding was confirmed through DNA analysis.

The aggressive pigweed species is native to the desert regions of the Southwestern U.S. and northern Mexico, but it has slowly spread to Southeastern and Midwestern states, where it has become a major threat to cotton, corn and soybean crops. In recent years, it has moved into South Dakota, Minnesota and Iowa.

It can grow as much as 3 inches per day and as tall as 7 feet, with each plant producing hundreds of thousands of seeds. The threat from Palmer amaranth is so great that North Dakota State University Weed Science officials named it the “weed of the year” in both 2014 and 2015, even though it hadn’t yet been found in the state.

A heavy Palmer amaranth infestation can cut soybean yields by as much as 79 percent and corn yields by up to 91 percent, according to research by Purdue University .

In Iowa, where the weed was first found in 2013, it’s a threat to corn crops, though so far “it hasn’t taken over as some people thought it would,” said Bob Hartzler, a professor and weed expert at Iowa State University.

That’s because many fields are infested with waterhemp, a relative, and farmers have been aggressively targeting that weed.

But Palmer amaranth is still slowly getting a foothold in the state.

“It’s something to keep an eye on, and if we can find it early and target our control programs, I think we can save ourselves a lot of headaches down the road,” Hartzler said.

North Dakota Agriculture Commissioner Doug Goehring also said early detection is key.

“We are thankful it was found and encourage farmers and the public to learn to identify Palmer amaranth in order to react quickly to control the weed,” he said.

It can spread in a number of ways, including on farm machinery, in grass seed and even through the movement of wild birds.

“We do not believe the plants originated from contaminated seed mixes in this case, but believe it may have been introduced by wildlife,” Goehring said. “We are working with the North Dakota State Seed Department and NDSU Extension to identify other sources.”

Palmer amaranth has developed resistance to some types of herbicides, but options are still available, according to Hartzler.

“One thing pigweeds do is adapt very quickly,” he said. “That’s why we try to encourage everybody to really go after it hard when they first spot it and try to prevent it from getting established.”