Pigweed Species Farmers Need to Know

By Scout Nelson

North Dakota crop specialists highlight the importance of correctly identifying pigweed species as these weeds continue to spread across many fields. Proper identification helps farmers and crop advisors build effective management plans, reduce herbicide resistance risks, and protect crop yields. Learning key plant differences allows producers to make better decisions for long-term weed control.

Several pigweed species appear similar, but each has unique traits. Waterhemp is known for having the smallest seed among North Dakota pigweeds. It has narrow leaves, very little hair, and long, thin flower spikes. Plants may show red, green, or mixed stem colors, and male and female flowers grow on separate plants.

Tumble pigweed has narrow cotyledons with pointed tips and small spoon-shaped leaves. It grows many branches near the base and often breaks off at the soil line, allowing the plant to tumble. This species has no hair and carries both male and female flower parts on the same plant.

Palmer amaranth is another important species. It has narrow, uneven cotyledons and ovate leaves with long petioles. Some leaves may show a white mark. The plant has no hair and produces very long flower spikes with sharp seed bracts that can feel painful when touched.

Redroot pigweed stands out because of its dense hair on stems and petioles. The base of the stem often appears dull red. It forms short, thick flower spikes and carries male and female flower parts close together.

Powell amaranth looks similar to redroot but has fewer and shorter hairs. Its stems often show a darker red color that extends higher up the plant. The flower spikes are long and wide, with sharp seed bracts.

Prostrate pigweed has the largest seeds and grows flat along the ground. It has wide, shiny cotyledons and spoon-shaped leaves that stack closely at first. Flowers usually grow at the nodes, and stems are often dark red.

Extension specialists encourage farmers to learn pigweed biology and monitor herbicide resistance in their area. Accurate identification and early action help reduce weed pressure and support better crop management.