Abstract
Amaranthus palmeri has been sighted on only a couple of occasions in southwestern Idaho since 2021. These were isolated incidents and plants were either pulled or otherwise destroyed. In July 2023, staff of Amalgamated Sugar discovered a large patch bordering a potato field in southwest Idaho. Within days of this discovery, Agricultural Staff at Amalgamated Sugar, in collaboration with University of Idaho and Oregon State University staff conducted a full-scale survey of southern Idaho and eastern Oregon to help identify additional populations of A. palmeri. As of the end of 2023, 71 populations of A. palmeri had been identified and 23 sampled for genetic confirmation and resistance testing. Additionally, 4 populations of Amaranthus tuberculatus were discovered in sugar beet fields in southern Idaho. These populations were also sampled and analyzed. As of the end of 2024, 107 populations of A. palmeri and 4 populations of A. tuberculatus have been identified in southern Idaho and eastern Oregon. Nearly all A. palmeri populations sampled tested positive for glyphosate resistance, and some also containing ALS resistance. All populations of A. tuberculatus were positive for glyphosate resistance and only one containing additional ALS resistance. Additional resistance screening is ongoing at University of Idaho to determine additional HRAC group resistance in A. palmeri populations in Idaho. This discovery represents a distinct challenge for sugar beet growers in southern Idaho and eastern Oregon.
