Timeline of Palmer amaranth (Amaranthus palmeri) invasion and eradication in Minnesota

Abstract

Palmer amaranth–a fast-growing, challenging to control noxious weed that significantly reduces crop yields—was first found in Minnesota in September 2016 in conservation plantings sown with Palmer amaranth contaminated seed mixes. Minnesota Department of Agriculture (MDA) designated Palmer amaranth as a Prohibited Noxious Weed in 2015 and listed it as a Noxious Weed Seed in 2016 by emergency order. A genetic test to identify Palmer amaranth was simultaneously developed by multiple labs providing a tool to limit its spread as a contaminant in seed. Seed companies adopted genetic testing methods for labeling seed for sale reducing introductions via the seed pathway. Additionally, MDA determined that manure spread on crop fields from contaminated screenings fed to livestock resulted in new infestations. Limiting spread via these and other potential pathways was critical to successfully reducing the impact of Palmer amaranth. MDA, University of Minnesota (UMN) Extension, Conservation Corps Minnesota and Iowa (CCMI), farmers, and other partners are working to eradicate these infestations before they can spread. In 2016, 35 sites were sown with Palmer amaranth contaminated seed mixes. Palmer amaranth was found at eight (23%) of these sites. Management with intensive scouting, torching, prescribed burning, and herbicide application was implemented in 2016 and 2017. By 2018, no Palmer amaranth was found at any of these sites. Similar success to newer infestations in 2018, 2019, and 2020 was achieved using the same methods. MDA recorded management activities and documented a comprehensive timeline of Palmer amaranth in Minnesota. This timeline provides a story of success and challenges in combating and eradicating Palmer amaranth.

Multiple resistance to imazethapyr, atrazine, and glyphosate in a recently introduced Palmer amaranth (Amaranthus palmeri) accession in Wisconsin

“…Palmer amaranth dispersal has been attributed to natural and agricultural causes, including seed transport in waterfowl digestive tracts during migration (Farmer et al 2017), water movement (Norsworthy et al 2014), hurricanes (Menges 1987), use of weed-contaminated seeds for the Conservation Reserve Program (CRP; Hartzler and Anderson 2016), animal feed contaminated with seeds and subsequent manure applications (Hartzler and Anderson 2016;Sprague 2014;Van de Stroet and Clay 2019;Yu et al 2021), and movement of farm equipment (Hartzler and Anderson 2016;Sauer 1957;Werle et al 2019). Given its nature, characteristics, and confirmed resistance to many herbicide sites of action (SOA), the continued dispersal of Palmer amaranth could impose detrimental impacts on cropping systems in Wisconsin and neighboring states.…”

“…The indication that this recently introduced Palmer amaranth accession (BRO) in Wisconsin is likely to carry multiple herbicide-resistance traits is cause for great concern. The most notable source of new Palmer amaranth infestations in Iowa, Ohio, Illinois, and Minnesota was credited to the use of Palmer amaranth-contaminated seeds for CRP (Hartzler and Anderson 2016;Yu et al 2021). The 2021 State-Noxious-Weed Seed Requirements Recognized in the Administration of the Federal Seed Act (USDA 2021) designates Palmer amaranth as a prohibited noxious weed seed in Wisconsin, prohibiting the sale of agricultural seeds contaminated with Palmer amaranth seed.…”

“…Similarly, Iowa and Minnesota designate Palmer amaranth as a noxious weed, whereas Illinois and Michigan do not. Minnesota went beyond and now requires a genetic test of any Amaranthus contaminant to determine if Palmer amaranth is present in agricultural seeds (USDA 2021;Yu et al 2021).…”

“…Animal feed contaminated with Palmer amaranth seeds and subsequent manure applications have been reported as a possible cause of Palmer amaranth spread. In 2018, the Minnesota Department of Agriculture identified animal feed and manure as pathways for the introduction of Palmer amaranth in the state, after contaminated sunflower feed was used for cattle (Yu et al 2021). Whole cottonseed is another example of a low-cost by-product with good nutritional value commonly used in dairy diets (Warner et al 2020).…”

Comparison of methods to recover amaranth weed seeds from manure

“…Long distance spread primarily occurs through contaminated seed or animal feed, notably via conservation seed plantings, livestock manure, and transfer of used farm equipment for custom harvesting or through sales (Davis et al., 2015; Kistner & Hatfield, 2018; Schoeck, 2018). For example, recent cases of Palmer amaranth detection in the Upper Midwest were the result of contaminated livestock feedlot manure being land applied after animals were fed contaminated sunflower ( Helianthus annuus L.) or cotton ( Gossypium hirsutum L.) screenings that were imported from out of the region (Yu et al., 2021; Rodrigo Werle, personal communication, 12 Aug. 2020). This pathway is concerning for northern regions attempting to limit the introduction and spread of Palmer amaranth, particularly those with large livestock populations that may import feed from regions infested with this weed.…”