May 9, 2022
Marcelo Zimmer, Weed Science Program Specialist
Department of Botany and Plant Pathology, Purdue University
Palmer amaranth is an aggressive, invasive weed native to the desert regions of the southwest United States and northern Mexico. It slowly spread throughout the United States and is currently ranked as the 4th most common weed present in broadleaf crops, fruits and vegetables in the U.S. and Canada, according to a 2016 WSSA survey. Palmer amaranth seed can be introduced to new areas in a multitude of ways including contaminated farm equipment, beef or dairy manure, hay bales from contaminated fields, migratory birds, etc. Once Palmer amaranth seeds are introduced into a new field, this weed can quickly establish and become challenging to control.
Palmer amaranth was ranked as the most troublesome to control weed in broadleaf crops. Its success as a weed can be attributed to several features, including genetic diversity, prolific seed production (100,000 to half a million seeds per plant), rapid growth (up to 3 inches a day), herbicide resistance (resistance to 8 modes of action reported), and extended period of emergence (from early May until mid-September). Although challenging to control, Palmer amaranth can be managed using Integrated Pest Management (IPM) strategies, such as crop rotation, deep tillage in heavily infested fields, cover crops, applying multiple effective herbicide modes of action, overlapping soil residual herbicides with postemergence applications, hand-weeding escapes, monitoring ditches and borders of fields, and harvesting heavily infested fields last.
Heap I (2019) The International Survey of Herbicide Resistant Weeds. Available: http://www.weedscience.org. Accessed May 9, 2019
Legleiter T, Johnson B (2013) Palmer amaranth biology, identification, and management. Purdue Extension. https://www.extension.purdue.edu/extmedia/WS/WS-51-W.pdf 13 pages
Van Wychen L (2016) 2016 Survey of the Most Common and Troublesome Weeds in Broadleaf Crops, Fruits & Vegetables in the United States and Canada. Weed Science Society of America National Weed Survey Dataset. Available: http://wssa.net/wp-content/uploads/2016-Weed-Survey_Broadleaf-crops.xlsx