While a rancher found Palmer amaranth in his field in Grant County, for the most part, those in western region of North Dakota are still learning what the weed looks like.
At the Western Crop and Pest Management School, Ryan Buetow, NDSU Dickinson Research Extension Center (DREC) cropping systems specialist, talked about the weeds on everyone’s minds – waterhemp, redroot pigweed, Powell amaranth and Palmer amaranth.
“When you are doing Integrated Pest Management, it is important to properly identify your pest, scout and know your weeds,” Buetow said.
Redroot pigweed has a typical pigweed shape, short hairs on the stems, and most often, a short petiole. When it heads out, it has a stubby seed head.
Waterhemp has shorter, narrower leaves than pigweed. It is smooth and “waxy” looking.
“Waterhemp is an issue out east and I can see it working its way out west, slowly following soybeans,” he said.
Prostrate pigweed has a typical pigweed shape, but it lives close to the ground.
With redroot pigweed, there are short, dense hairs, but the petiole can be long on mature plants.
Powell amaranth has short, dense-to-sparse hairs, and is sometimes confused with Palmer amaranth. Powell is a monoecious plant.
Tumble pigweed looks like kochia from a distance.
“You get closer and you see those leaves which look like pigweed,” Buetow said. “The shape is like a tumbleweed that is going to blow across the fields.”
Palmer amaranth can sometimes have watermarks and has no hair.
“It can get real big, so think of all the nutrients and moisture it is taking up,” he said.
A very large Palmer stem could be damaging to a combine.
“Don’t use redroot pigweed as an identification for Palmer amaranth because a lot of pigweed can have that reddish color,” Buetow said.
Palmer can come in with millet seed, so be careful when getting cover crop seed. It can come in on railroad cars, custom combines and equipment.
“It really is not that far away, so be sure you are scouting for it. It can be small, so be careful when you pull it because of the seeds,” he said.
Palmer and waterhemp have no hairs, while redroot pigweed and Powell do.
“One of the keys to Palmer is the long petiole which can be longer than the leaf itself,” he said. “Both Palmer and waterhemp are dioecious like some varieties of hemp, with both male and female plants.”
With Palmer, female plants will be spikier along the bracts.
Waterhemp has a more narrow leaf shape.
“Waterhemp and Palmer amaranth can adapt very quickly and take on those herbicide resistant traits,” he said.
Information from Kansas State University shows that 14 days after planting soybeans, Palmer amaranth was almost as tall as the soybean plants. Within 20 days, it outdistances the soybean plant, and no one can even spot the soybean plants anymore.
“That pre-emergent herbicide is going to be so important for you if Palmer becomes an issue for you,” Buetow said.
The earlier herbicide is applied, the better the control.
“Once Palmer gets going, make sure you are applying your herbicide early, because once it gets past a certain height, your control will be very limited,” he said.
Palmer is the only weed that can currently drive a “farmer out of business and a single weed is too many.”
“A zero tolerance approach is the only way to go with Palmer because it puts out a lot of seeds (1-2 million seeds per plant),” he said. “It grows very aggressively from 6-8 feet tall and reduces yield 91 percent in corn and 79 percent in soybeans.”
If one plant is allowed to go to seed, it can take over a field very quickly, and it can be herbicide resistant.
“People think it is only a problem in the eastern part of the state because of the moisture, but it can grow just as easily in the desert,” he said.
Waterhemp is a nuisance, but Palmer amaranth is a “complete game-changer.”
Palmer seed head is longer than other pigweeds, and Palmer is more of an issue in cropland. In rangeland, there is usually not enough competition for it.
A key identifier is the long petiole and no hairs.
Dicamba is a tool farmers can use, but it’s a tool that needs to be managed correctly.”
“We need our blood to live and plants need processes to live. Herbicide attacks a single or multiple points inside a plant. Over time, if you attack the same point, the plant adapts,” Buetow said.
Don’t use the same trait over and over.
Economically, it costs $48 per acre to control kochia, but it costs $148 per acre to control Palmer amaranth. Palmer comes up throughout the growing season.
“It can be very expensive to manage Palmer once it gets out of hand,” he said.
The North Dakota Department of Agriculture website explains how to handle Palmer, recommending to not dig up the plant, but call the county Extension agent or county weed officer.
Marestail or horseweed is the weed of the year. After its rosette, the plant bolts up and it does thrive in no-till. It is a winter annual, so a fall application is important, as well as a spring burndown.
Houndstongue is not a noxious weed anymore. It is found in tree rows and along fencelines. A lot of spurs can attach to cattle and the leaves smell like popcorn. The first year it is a rosette, with velvet leaves. 2-4-D should handle the rosettes.