Palmer amaranth has a long history of herbicide resistance that dates back to 1989 when the first plants resistant to the Group 3 herbicide Treflan (trifluralin) in cotton and soybean fields were identified in South Carolina. Populations resistant to 9 herbicide groups (Groups 2, 3, 4, 5, 9, 10, 14, 15, 27) have since been identified in alfalfa, corn, soybean, sorghum, peanuts, orchards, and other settings in various states. Palmer amaranth is currently the number one weed problem of crops in the southwestern, southeastern, midwestern, and the Great Plains regions of the United States.
The future of agriculture in the PNW could be upended by the appearance of Palmer amaranth in the region, with a potential to greatly disrupt weed management programs in various crops. In fact, it appears that Palmer amaranth is already in the PNW region, albeit in isolated areas. A photograph (Figure 1) taken by Bonnie Davis, Washington County, ID Weed Superintendent seems to be of Palmer amaranth plant. The photograph was taken in an area south of the City of Weiser, ID. We will monitor the surrounding fields during summer 2022.
What could you do to avoid expansion of Palmer amaranth in the region?
The first action is correct identification of the weed. The bulletin mentioned above contains images that could help identify Palmer amaranth. Most weed introductions can be kept to a minimum with vigilance and proactive scouting of fields to uproot plants before setting seeds. Consider bringing plants suspected of being Palmer amaranth to your Extension Office and sending photographs to weed scientists at Oregon State University, University of Idaho, or Washington State University. Always include georeferencing information to enable easy identification of the area.