Montana State University issued an Ag Alert on Thursday after a Palmer amaranth plant was confirmed for the first time in Hill County, Montana in August 2025. It would be the fourth confirmed occurrence of this weed in Montana, some suggesting it may have come from a custom harvester visiting from outside the state.
The first discovery of Palmer amaranth was in Carter County in September 2024, and photographed by Amanda Williams of the Carter County MSU Extension. “I saw the plant growing along the highway when I was going to the family ranch to work for the weekend,” Williams recalled. “I took some pictures, took the plant, and sent both off to the Weed and Invasive Plant Ecology and Management Group in Bozeman.”
The discovery underscores the urgent need for growers across Montana to stay vigilant against this invasive pigweed. According to the MSU Ag Alert, early detection and rapid response are critical to containing Palmer amaranth before it spreads and establishes permanent populations. Williams emphasized that community awareness was vital after her 2024 find. “Thankfully we just had one male plant, so it didn’t produce any seeds,” she said. “After we got confirmation, we did a lot of work talking to producers in the area to educate them. Our community has done a good job of being vigilant toward this weed, and many others. They understand that early detection and rapid response is very important to stay in front of any invasive species.”
Palmer amaranth is considered one of the most troublesome pigweed species in the United States. It can reduce crop yields, spread quickly across fields and regions, and develop resistance to multiple herbicides. The MSU Ag Alert warns that because of these challenges, producers, agronomists, and landowners should learn how to identify both Palmer amaranth and waterhemp (Amaranthus tuberculatus), as well as recognize the pathways through which they spread, such as contaminated equipment, feed, or seed.
Identification can be difficult since pigweed species often look similar. The MSU Ag Alert points growers to MontGuides and other resources that provide photos and tips to distinguish Palmer amaranth and waterhemp from other pigweeds. Swift recognition, the alert notes, can make the difference between quick eradication and costly long-term management.
Resources for Identification and Management:
- MT Department of Ag – Early Detection Rapid Response Palmer Amaranth Page
- MSU MontGuide: Palmer Amaranth
- Palmer Amaranth MontGuide
- Waterhemp MontGuide
- NDSU Palmer Amaranth Webpage
The Bottom Line
Montana has so far avoided widespread infestations of Palmer amaranth, but the Carter County case shows how easily it can appear. According to the MSU Ag Alert, vigilance, reporting, and rapid action are key to protecting pulse crops and other agricultural systems across the state.
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