Should I be concerned about Palmer amaranth in my prairie strips?
Palmer amaranth is a noxious and aggressive weed you should keep watch for in your crop environment, but you need not be overly concerned about it in your prairie strip.
Around 2016, Palmer amaranth was unintentionally brought into Iowa on agricultural equipment and within seed mixes for native plantings as well as in cotton seed and gin trash used in dairy rations. Additionally, some seeds of this species could have come in via hay and/or livestock bedding. It's arrival is concerning because it is difficult to control in the crop environment and can negatively affect production.
The good news is that native seed dealers now know to watch for out Palmer amaranth and work keep it out of their mixes. Using local ecotype seed -- seed grown within 100 mi north/south and 200 mi east/west of your planting site -- reduces the chance of receiving seed contaminated with Palmer amaranth (while also improving the establishment success of the native plants). Furthermore, Palmer is an annual, not a perennial like the native plants that comprise prairie strips, and with diligence it can be eradicated from any given site. And finally, the Palmer amaranth that did show up in Iowa did not appear to have cold-hearty seeds. As long as Iowa's winters are cold, this weed does not appear to be a big problem here compared to the Southern US.
Resources are available to help identify and eradicate Palmer amaranth. The ISU Extension Store hosts a brochure and accompanying video to assist with differentiating Palmer amaranth from related species in Iowa: waterhemp and other problematic pigweeds. Early detection is imperative for stopping this weed.
The first defense against Palmer amaranth and many other aggressive weeds within your native planting is to purchase amaranth-free prairie seeds from a reputable seed dealer. Reputable seed dealers will regularly scout their production fields and remove weedy plants before they go to seed.
The second defense against Palmer and other aggressive weeds is to establish a competitive stand of native plants. This STRIPS brochure summarizes the steps needed to do so. Regular scouting and mowing during the establishment phase are critical to establishing the desirable native plants, and preventing weeds like Palmer amaranth from reproducing. Once the native prairie community is well-established, there is little to no room for annual weeds to take root and grow. Well-established prairie communities commence growth in the spring before Palmer amaranth germinates and will continue to compete effectively against annual weeds year after year.
If you believe you have Palmer amaranth, this USDA NRCS Tech Note, Eradicating Palmer amaranth on Tallgrass Prairie Restorations, details the steps to eradicate the weed. We encourage you to seek guidance from local USDA NRCS Field Office staff, ISU Extension Agronomists, or a Certified Crop Advisor.