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A deep-rooted fear

Palmer amaranth, the herbicide-resistant species of pigweed known for devastating crops across the South and Midwest, has been found in North Dakota for the first time.

Palmer amaranth, the herbicide-resistant species of pigweed known for devastating crops across the South and Midwest, has been found in North Dakota for the first time. Submitted photo
Palmer amaranth, the herbicide-resistant species of pigweed known for devastating crops across the South and Midwest, has been found in North Dakota for the first time. Submitted photo

Palmer amaranth, the herbicide-resistant species of pigweed known for devastating crops across the South and Midwest, has been found in North Dakota for the first time.

Laboratory analysis confirmed Monday that a plant found in a row-crop field in McIntosh County in South-central North Dakota is Palmer amaranth.

"Palmer amaranth's prolonged emergence period, rapid growth rate, prolific seed production, and propensity to evolve herbicide resistance quickly makes this the most pernicious, noxious and serious weed threat that North Dakota farmers have ever faced," Rich Zollinger, retired NDSU Extension weed scientist, said.

The unidentified farmer who first discovered the weed pulled the plant and it ultimately ended up with NDSU weed specialists, who confirmed it.

"We just don't have the experience with it that we'd like," Greg Endres, NDSU Extension agronomist, said.

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Palmer amaranth is, without question, the most prevalent weed concern in the U.S. according to agronomists and weed specialists alike. A type of pigweed that originated in the desert region of northern Mexico, Palmer subsequently spread through the Mississippi Delta. Within a few years the plant invaded and destroyed crops across Missouri, Kansas, Iowa, Wisconsin, Minnesota and South Dakota.

Suspected growth has been uncovered in five North Dakota counties: Benson, Dickey, Foster, McIntosh and Richland, Endres said. The North Dakota Department of Agriculture confirmed on Monday that the find in McIntosh County was, in fact, Palmer amaranth and likely came from seeds dropped by migratory birds, according to a press release.

"The Benson case was most likely introduced to the county by railroad car and the Richland case most likely came in with livestock feed," Endres said. "The method of introduction of the weed in each case has been difficult to determine, but it appears that each case is unique with that regard."

Palmer amaranth poses a significant threat to North Dakota crops because it can grow two to three inches per day in optimum conditions and reach heights of eight feet. A single plant is known to produce up to a million seeds, quickly spreading the noxious weed great distances. With wind conditions notorious in North Dakota, the weed could potentially spread across the state with rapid pace.

The root system has been known to reach diameters equivalent with that of a baseball bat, posing serious risk of combine header damage during harvest, if unnoticed.

Heavy infestations recorded in other states show reductions in yield of nearly 80 percent for soybeans and over 90 percent for corn.

Further complicating the issue is that Palmer amaranth is notoriously difficult to control as the weed is prone to resist nearly all common herbicides.

"Palmer amaranth is an extremely rapid-growing species once it emerges," Endres said. "It's easy to calculate that we don't have much time to make an application, assuming we find it while it's in its early stages, which is problematic, considering it's extremely difficult to identify the weed when it's in its earliest stages of growth."

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Unlike other annual weeds that need to be controlled only through early summer, Palmer amaranth emerges throughout the growing season and into harvest, Endres noted.

Identifying Palmer can be difficult because it resembles multiple other species of weeds, including redroot pigweed, Powell amaranth and waterhemp - all of which can be treated with common herbicide. One of the best ways to distinguish Palmer amaranth from the other weeds is its leaf stem, or petiole, Endres said. Palmer amaranth's petiole is as long as, or longer than, the leaf blade.

It is expected that Palmer amaranth will be added to the noxious weeds list following the confirmation of the McIntosh case.

Farmers are urged to work with local weed officers, extension agents and other experts to identify and report suspect plants. Palmer amaranth may spread through multiple channels, including contaminated seed mixes, equipment and machinery movement, animal feed and bedding, and wild birds.

NDSU Extension plans to host meetings with area landowners to discuss scouting techniques and how to report suspect Palmer finds. Details of those meetings will be announced at a later date.

Anyone who sees a plant they believe may be Palmer amaranth should contact a local NDSU Extension agent or agronomist as soon as possible. More information can be found online at www.ag.ndsu.edu/extension/directory .

Related Topics: AGRICULTURE
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