Keep an eye out for Palmer amaranth hitching a ride into Minnesota via contaminated feed ingredients. Minnesota has at least one infestation in the state which arrived via contaminated cattle feed. The potential for this to happen again is high, especially when sourcing feed ingredients from areas where Palmer amaranth and other problematic weeds are more common.

Pay attention to weeds growing around livestock feeding areas, near manure storage areas, or in fields with a history of manure application. These are likely the areas where Palmer amaranth and other new weeds will show up first.

While weeds can find their way to your farm via wildlife and other uncontrollable factors, many new weed seeds are brought onto the farm from normal farm activities. Most of the new infestations of Palmer amaranth have been brought in via equipment (especially used equipment purchased from an area where Palmer amaranth is more common), contaminated seed, or contaminated feedstuffs. The amount of risk for contamination with weed seeds depends on the type of feed and where it originates. Feed that has been ground, pelletized, or ensiled is less concerning compared to less-processed feed ingredients.

Palmer amaranth is more common further south. Any feed ingredient which was produced where Palmer amaranth is present in fields is more likely to become contaminated. Cottonseed and sunflower screenings have been the source of several infestations in the Midwest. Other feed ingredients, including hay and animal bedding, produced where Palmer amaranth is more common are also concerns. Additionally, herbicide resistance is more common further south, meaning other weed seeds that may travel in with the feedstuffs, including waterhemp, may be herbicide resistant.  

Any forage produced in weedy fields will likely contain weed seeds, whether harvested as dry hay or ensiled. Ensiling forages will help reduce the viability of weed seed. This is especially the case for grass weed seeds. Even hard-coated seeds like pigweed can be degraded during ensiling. Palmer amaranth seed viability can drop by 40-60 percent after one month of ensiling alfalfa or corn silage.

Don’t assume animal digestion will kill all of the seeds.Though it will reduce weed seed viability, feeding contaminated feed to livestock will not eliminate all Palmer amaranth seed. Grass and soft-coated broadleaf seeds are more easily destroyed in digestion than hard-coated seeds like Palmer amaranth. In ruminants like cattle, nearly 30 percent of amaranth seed survives digestion. The gizzard digestive system of poultry is highly effective at destroying weed seeds. For instance, only 3.5 percent of Palmer amaranth seeds fed to ducks were recovered and found viable.

Internal heat generated by properly composted manure will kill most weed seeds — even Palmer amaranth. Aged manure is not composted manure. Weed seeds are killed in composted manure due to warm temperatures ( greatere than 140 F) for several days. In typical on-farm composting sites, weed seed viability is typically reduced by more than 90 percent. This percentage is even higher in the best-managed compost sites.

More information on Palmer amaranth in manure, visit  https://blog-crop-news.extension.umn.edu/2019/06/palmer-amaranth-in-manure-what-can-you.html

Palmer amaranth is a highly competitive pigweed closely related to waterhemp. Like waterhemp, Palmer amaranth emerges throughout the growing season, and can grow 2-3 inches per day, causing large yield reductions if it goes uncontrolled. Control is often challenging, as Palmer amaranth has resistance to many different herbicides. Palmer amaranth is on Minnesota’s prohibited noxious weed eradicate list. For more information and tips on identifying this weed, visit https://extension.umn.edu/annual-broadleaf-weeds/preventing-palmer-amaranth-minnesota.

If you suspect Palmer amaranth on your farm, please contact one of the parties listed below.

Arrest the Pest — web: http://www.mda.state.mn.us/plants-insects/arrest-pest; email: arrest.the.pest@state.mn.us; phone: (888) 545-6684.

Denise Theide, Minnesota Department of Agriculture — email: Densie.Theide@state.mn.us; phone: (651) 201-6531

Anthony Cortilet, Minnesota Department of Agriculture — email: Anthony.Cortilet@state.mn.us; phone: (651) 201-6538

Shane Blair, Minnesota Department of Agriculture — email: Shane.Blair@state.mn.us; phone: (507) 884-2116

Bruce Potter, University of Minnesota Extension — email: bpotter@umn.edu

This article was submitted by Nathan Drewitz, Jared Goplen, Adam Austing, and Chryseis Modderman, University of Minnesota Extension.