Published August, 2009

Name: Spiny pigweed/Spiny amaranth 

Scientific name: Amaranthus spinosus L. 

Life Cycle: Warm season annul 

Origin: Tropical America 

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 may reach 3 feet tall. Sharp spines that inhibit grazing are found in axils of stems and are surrounded by a dense cluster 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 seeding. Consult your local Cooperative Extension Service personnel (http://ces.ca.uky.edu/ces/) for herbicidal control in your area.--William W. Witt, PhD, University of Kentucky Department of Plant and Soil Sciences