Amaranthus palmeri S. Watson

Palmer Amaranth

Identification

Palmer Amaranth

Amaranthus palmeri S. Watson

Life cycle: Summer annual
Height: 6 to 8 ft

Palmer amaranth is a summer annual that emerges from seed throughout the growing season in North Dakota. The plant commonly grows 6 to 8 feet tall. Leaves are smooth, 2 to 8 inches long, alternate, and lance or egg shaped. A whitish V shaped or thumbprint mark is found on the leaves of some plants, but not all. The flowers are green, not showy, and end in three spiny bracts. Seed head spikes can be up to 3 feet long, and the female flowers are very prickly.

Palmer amaranth has reduced yield by up to 91 percent in corn and 79 percent in soybean. The weed has wide genetic diversity, which lets it adapt to new environments and has enabled it to develop resistance to many herbicides used on pigweed species. Early identification and eradication are the best way to keep it from becoming established in North Dakota.

Control

Controlling palmer amaranth

Best timing: Spray foliar herbicides before plants are taller than 2 to 3 inches. A preemergence herbicide is crucial.
Mowing and pulling: Pull plants from sites with no history of it, bag them, then burn or compost. Use certified weed free seed and rotate soybean with wheat, corn or perennial forage. Mowing does not work because plants regrow and set seed.
Herbicide: Moderate to heavy infestations need at least two herbicide applications. North Dakota populations have confirmed resistance to glyphosate, ALS inhibitors, HPPD inhibitors, atrazine, 2,4-D and dicamba.
Biological control: None is available.

Always follow the product label, and check rates in the North Dakota Weed Control Guide from NDSU. Your county weed control officer can tell you what fits your land. Source: NDSU Extension W1411 (December 2025).

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