November Weed of the Month: Palmer Amaranth

November’s Weed of the Month is Palmer amaranth (Amaranthus palmeri). This fast growing weed has developed resistance to multiple herbicide modes of action so it is difficult to control. Palmer amaranth produces a lot of seed, up to 250,000 per plant, and is highly competitive. It spreads quickly and will cause extensive corn and soybean crop losses.

Palmer amaranth is native to the arid southwestern United States and northwestern Mexico. It was accidentally introduced to the southeastern United States and became the most troublesome weed in cotton production, by far. It developed resistance to many herbicides with multiple modes of action and spread to row crop fields in much of the eastern half of the country. This dreaded weed was discovered in Minnesota in 2016.

Palmer Amaranth weeds

Palmer amaranth plant with seed spikes. (photo provided by the Minnesota Department of Agriculture.)

Palmer amaranth can be distinguished from closely related waterhemp and other pigweeds by a long petiole length and very tall flower and seed spikes. Unlike other pigweeds, Palmer petioles are often longer than the leaf blades. A petiole attaches a leaf to a stem. The flowering spike is much longer than that of other pigweeds. Leaves of some Palmer plants have a whitish V-shaped mark on them. Palmer amaranth is a summer annual that commonly reaches heights of 6-8 feet but can reach 10 feet.

If you find this plant, please report immediately by calling the Arrest the Pest at 888-545-6684 or emailing arrest.the.pest@state.mn.us.

Palmer amaranth detected in Minnesota

 ST. PAUL, Minn. – Crop scientists at the University of Minnesota and officials at the Minnesota Department of Agriculture (MDA) urge farmers to check fields for Palmer amaranth, an aggressive weed that can put corn and soybean crops at risk. A plant detected in a native seed planting plot on a Yellow Medicine County farm was confirmed today to be Palmer amaranth. This is the first confirmation of the weed in the state.

The MDA asks possible infestations to be reported by contacting the MDA’s Arrest the Pest line by phone at 1-888-545-6684 or by email at arrest.the.pest@state.mn.us. Landowners are encouraged to email photos of suspected infestations for identification.

“We encourage landowners to scout fields now before harvest for Palmer amaranth and report any possible infestations to the Minnesota Department of Agriculture,” said Geir Friisoe, MDA’s Director of Plant Protection. “The quicker we’re able to identify and start managing this weed, the better our chances will be to minimize the impact to our ag industry.”

Palmer amaranth

Palmer Amaranth has been found in Minnesota and the Department of Agriculture wants farmers to keep an eye on their fields to help nip this in the bud before an infestation can occur. (Photo by Bruce Potter)

 

Palmer amaranth can grow 2 to 3 inches a day, typically reaching 6 to 8 feet, or more, in height. Left uncontrolled, a single female Palmer amaranth plant typically produces 100,000 to 500,000 seeds. It is resistant to multiple herbicides.

It has been found in 28 other states, including Iowa, South Dakota, and Wisconsin.

“Palmer amaranth infestations have caused substantial yield losses and greatly increased weed management costs in cotton, soybeans, and corn in the southern states,” said Extension agronomist and crops leader Jeff Gunsolus. “This is a disconcerting, though not completely unexpected, discovery in Minnesota. We have been discussing proper identification procedures with crop consultants over the last three or more years.”

Close-up of Palmer amaranth

Palmer Amaranth has been found in Minnesota fields and it’s important for farmers to watch their fields in order to avoid an outbreak in farm fields across the state. (Photo by Bruce Potter)

 

Extension and MDA officials commend the grower and crop consultant who quickly contacted Extension after discovering a suspected Palmer amaranth plant. The weed is on MDA’s prohibited-eradicated noxious weed list, requiring all above- and below-ground parts of the plant be destroyed. Transportation, propagation or sale of the plants is prohibited.

MDA and Extension continue coordinating action steps to address the weed.

The MDA is investigating how the weed may have been introduced to the state.

In August, an Extension blog updated steps for both prevention and management at z.umn.edu/palamthbknd.

Further information is available at z.umn.edu/MDAPalmerAmaranth.