Amaranthus species are among the most troublesome weed species in agronomic production systems because of their innate ability to cause crop yield loss and their propensity to develop resistance to various herbicide site-of-action families. Several Amaranthus species are regarded as weedy pests across the Great Plains region, including the monoecious (male and female flowers on the same plant) species redroot pigweed (A. retroflexus), smooth pigweed (A. hybridus), Powell amaranth (A. powellii), tumble pigweed (A. albus), prostrate pigweed (A. blitoides), and spiny amaranth (A. pinosus), and the dioecious (separate male and female plants) species common waterhemp (A. rudis) and Palmer amaranth (A. palmeri). Among these species, smooth pigweed, redroot pigweed, Powell amaranth, Palmer amaranth, and the waterhemps are most common in Illinois corn and soybean fields. Historically, Palmer amaranth’s range was limited in Illinois but the species appears to be expanding its range in the state.
Soil Science Extension
University of Wisconsin Madison