Weed of the Month: Spiny Pigweed

Spiny Pigweed

Photo: University of Kentucky's College of Agriculture, Food, and Environment

Common name: Spiny pigweed, Spiny amaranth
Scientific name: Amaranthus spinosusL.

Life Cycle: Warm season annual
Origin: Tropical Americas
Poisonous: No

Spiny pigweed is distributed widely across the United States and grows most frequently along fence borders, feeding and watering areas, and other compacted areas. Spiny pigweed can sometimes infest entire pastures that are overgrazed. Seed germination occurs in late spring or early summer. Stems are reddish, stout, and branched. Mature plants can grow 3 feet tall and are most noticeable in late summer. Sharp spines that inhibit grazing are found in stem axils and are surrounded by dense clusters of female flowers. The male flowers are long terminal clusters.

Spiny pigweed control is relatively easy with herbicides when applied to plants less than 12 inches tall. Mowing and hand weeding are effective if done before flower production to prevent seed production. Consult your local Cooperative Extension Service personnel for herbicidal control in your area.

William W. Witt, PhD, a researcher in the department of Plant and Soil Science at the University of Kentucky, provided this information.

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