We returned late last week from a trip to southern Delaware where we participated in a twilight weed control tour at the University of Delaware Georgetown Research and Education Center. One of our take home observations was how widespread Palmer amaranth or pigweed was in that region.

Photo taken by W. Curran at Georgetown Delaware. Pigweed foreground is Palmer amaranth flower, while pigweed in rear is redroot pigweed.

Palmer amaranth was the dominant pigweed on the research farm. It is scary to think about how easily the seed could move between farms, counties, states, or regions with grain or other seeds, hay, soil, manure, equipment, etc. Coincidentally, the week before I received a phone call and a follow up email from one of our Pennsylvania agronomists who happened to pass by a soybean field in the southeast region and noticed an unusual looking pigweed. The agronomist decided to investigate, removed the plant(s) from the field, took some photos, and contacted me. I forwarded his images to colleagues in Delaware and Illinois and their response was that it was either Palmer amaranth or perhaps waterhemp. After my trip last week, those southeast PA images sure look similar to what I saw in Delaware. I don’t think the landowner is even aware of the potential problem averted.

The news gets worse. Mark Loux at Ohio State reports in this week’s CORN newsletter that a new Palmer amaranth infestation has been discovered in an area SW of Columbus. There is a dairy farm in the area that has been using cottonseed products from the South. The Palmer amaranth infests a number of fields in the area and growers are currently busy digging out and removing plants before they set seed. Palmer amaranth is now a state noxious weed in both Ohio and Delaware. The OSU weed science website has some additional information on Palmer amaranth, including a short video on identification and an 11-minute video that explains the risk from this weed.

Bottom-line, if you find plants that you believe to be Palmer amaranth, please contact us, your local county extension educator, and/or professional crop consultant. As Mark Loux states in CORN, if there are immature plants, there is still time to dig up or chop them down, and ideally also remove them from the field. However, once mature seed has formed the strategy changes from plant removal to isolation and remediation of infestations.