Palmer amaranth

This Palmer amaranth plant was the first one found in North Dakota. Photo courtesy of Bruce Kusler, farmer and Pioneer seed salesman.

The inevitable became a reality late this past August as Palmer amaranth, a very aggressive weed, was found in North Dakota for the first time in a row-crop field in McIntosh County in the southcentral part of the state.

While scouting his field and doing some hand-weeding, a farmer came across plants that looked unusual and considered the possibility it was Palmer amaranth. He pulled the plants to keep them from going to seed and showed the plants to a local agronomist, who contacted an NDSU weed specialist for confirmation.

It is believed the plant in McIntosh County likely came from seeds dropped by migratory birds, according to NDSU Extension sugarbeet agronomist Tom Peters.

It has been rumored the finding farmer was Bruce Kusler, a local farmer and Pioneer Seed salesmen, but Crystal Schaunaman, McIntosh County Extension agent wants to make it clear he wasn’t the farmer who first located the weed.

 “He’s just been an agronomist and seed dealer in the area who lives there,” she said. “I keep hearing his name pop up. He’s been there helping to talk to neighbors and get stuff done to help with the situation.”

Schaunaman was part of a group who scouted suspect fields and pulled plants. Those fields have since been combined and received post-herbicide applications to clean up any plants that may still be out there.

“We’ve also been scouting in other parts of the township, but that’s not to say other parts of the county shouldn’t be scouted as well because there were also some outliers,” she said.

Palmer amaranth is the number one weed problem in the United States. It’s a type of pigweed that originated in the desert region of the southwestern U.S. (New Mexico and Arizona) and northern Mexico, then spread to the Mississippi Delta before identification in Missouri, Kansas, Iowa, Wisconsin, Minnesota and South Dakota, as well as other states.

The weed poses a serious threat to North Dakota crops because it can grow 2-3 inches per day in optimum conditions and reach a height of 6-8 feet. A single plant can produce up to 1 million seeds. Especially heavy infestations have reduced yield up to 79 percent in soybeans and 91 percent in corn.

Palmer amaranth is also extremely hard to control because it tends to be resistant to several herbicides. Applying herbicides before the weed emerges is more effecting than trying to control it with herbicides after it has started growing.

When asked about farmers’ reaction in the county to the finding of Palmer amaranth, Schaunaman says the best way to describe the overall response is, “Holy crap!”

“The farmers in the area have been like, ‘Let’s do everything possible to try and get a handle on this thing so we can delay it as long as possible.’ There have been a group of folks working together and really helping each other out,” she said. “They’ve been scouting the area, hand-pulling, and giving each other advice.”

The finding of Palmer amaranth in the county began discussions that Schaunaman says should have been going on for a while now about water hemp control, such as using a variety of control methods rather than relying on just one during the planting season.

“We need to be rotating chemistries, as well as doing pre- and post-emergence and varying our weed control,” she noted.

Schaunaman says their strategy next spring is going to be about scouting and getting resources into the hands of farmers – making sure they know what they’re looking for and what measures to take against it.

Now that the weed has been found, producers’ next step is to find ways to prevent it from spreading.

Most of the Palmer amaranth plants that have been found have produced very little seed according to Brian Jenks, weed scientist at NDSU’s North Central Research Extension Center in Minot.

“It is possible that these plants germinated and emerged later than most weed seeds,” he said. “Ideally, these weeds would be pulled and removed from the field, however, we may not see every Palmer plant. Although a pre-harvest burn-down in soybeans is not common, it may stop or reduce seed production of plants that were missed.

 “If there were Palmer plants in the harvested field, the remaining stems still may regrow and produce seed if there is a delayed killing frost. Thus, a postharvest desiccation may be warranted to ensure zero seed production,” he added.

Palmer amaranth is known to be resistant to the herbicide glyphosate in other states, so the plants found in North Dakota probably are glyphosate-resistant, too. Thus, glyphosate likely will not be effective as a Palmer amaranth desiccant (drying agent).

Jenks says the burn-down solution Gramoxone may be less effective against Palmer amaranth because the rate for soybean desiccation (dryness is only 8-16 fluid ounces, which is lower than for other crops. Sharpen usually is more effective as a desiccant when tank-mixed with glyphosate, but given that Palmer amaranth plants found in North Dakota likely are resistant to glyphosate, Jenks does not recommend this mix.)

“A better option may be to tank-mix Gramoxone and Sharpen,” he said.

Here are some pre-harvest desiccant options:

- Gramoxone: 8-16 fluid ounces. Apply with NIS (nonionic surfactants). This has a 15-day pre-harvest interval (wait time between the application and when the crop can be harvested).

- Sharpen: 1-2 fluid ounces. Apply with AMS (ammonium sulfate) plus MSO (methylated seed oil). This has a three-day pre-harvest interval.

- Gramoxone (16 fluid ounces) plus Sharpen (2 fluid ounces) plus AMS plus MSO. This is the best option, according to Jenks.

Here are recommendations for post-harvest desiccant options.

- Gramoxone: 2 pints. Apply with NIS.

- Sharpen: 1-2 fluid ounces. Apply with AMS plus MSO.

- Gramoxone plus Sharpen plus AMS plus MSO

- Gramoxone plus 2,4-D plus NIS

Jenks suggests producer apply these chemical at a spray volume of 20 gallons per acre to obtain adequate coverage. He also cautions producers not to use Roundup or Sharpen pre-harvest on soybeans grown for seed.