May-June 2024 issue

Volume 57, Issue 3

Palmer amaranth is one of the most troublesome pigweeds in crop production systems in the United States. It only recently started to appear in the Pacific Northwest (PNW). A coordinated extension and outreach effort was launched to track Palmer amaranth in the PNW. In 2023, tissue samples were collected from pigweeds suspected to be Palmer amaranth with tests providing confirmation. Palmer amaranth was detected in several crops as well as right-of- way and private property. Most of the Palmer amaranth populations were confirmed to be resistant to glyphosate. Additional surveys and resistance screening efforts are underway to map the distribution of Palmer amaranth and assess the level of herbicide resistance across the region. The cover image shows one identifying feature of Palmer amaranth, which is not seen with other pigweeds, namely, that its petiole (the stemlike structure that connects the leaf blade to the main stem) can be more than 3 inches long, which is longer than the leaf blade.