Pigweeds are among the most difficult weeds to manage in row crop systems due to their rapid growth, high seed production and widespread herbicide resistance. During the past two decades, reliance on herbicides for weed management has led to the evolution of resistance in Palmer amaranth populations to several herbicides, particularly ALS -- acetolactate synthase -- glyphosate and PPO-inhibitors. That reality has intensified the need for integrated weed management strategies, including non-chemical practices such as cover crops.
Recent research from the University of Nebraska–Lincoln sheds light on how cover crop management decisions such as planting time, species selection and termination timing influence pigweed -- Palmer amaranth, waterhemp, redroot pigweed and smooth pigweed -- suppression. In a comprehensive meta-analysis of 41 field studies conducted across the United States and Canada from 1994 to 2024, researchers evaluated how various cover crop strategies affected the density and biomass of pigweed species, with an emphasis on Palmer amaranth, waterhemp, redroot pigweed and smooth pigweed.
Cover crops work, decisions matter
The meta-analysis, which included more than 100 site-years of data from across the United States and Canada, found that cover crops significantly reduce pigweed emergence and growth. However, their effectiveness depends on how and when they are managed.