What does this mean for growers in the Dakotas and Minnesota? Since this weed is not known to be present in the Upper Midwest yet, rapid early detection and eradication before any permanent population can become established is key, says Lisabeth Stalh and Jeff Gunsolus, University of Minnesota extension specialists.
Remove suspect plants before they can produce seed; that will help prevent Palmer amaranth from becoming a long-term problem.
Palmer amaranth has been the bane of growers in the South for some time. In recent years, populations of Palmer amaranth have been found more to the north in Nebraska, Illinois, Wisconsin, Indiana, Ohio, Michigan, and now in Harrison County, Iowa, near the Missouri River.
•It's been called a weed-management "game changer" for several reasons:
•It's competitive, with reported yield losses up to 78 percent in soybeans and 91 percent in corn.
•It grows quickly - up to three inches a day.
•It produces large amounts of seed.
•It has the propensity to resist glyphosate and other classes of herbicides.
Although Palmer amaranth looks similar to waterhemp and other pigweed species, some key identifying characteristics include long leaf petioles (stalk that attaches the leaf to the stem) and a long, unbranched inflorescence (seed head) that is prickly to the touch.
This is a good time of year to identify Palmer amaranth. Purdue University released "Identifying Palmer Amaranth in the Field," a video to assist in identification.
Growers in the Upper Midwest at greatest risk of a Palmer amaranth infestation include those that feed cottonseed meal or "gin trash" to their animals. Since Palmer amaranth is widespread in cotton-producing areas of the South, cotton-related feed sources could be contaminated with Palmer amaranth seed. Not all weed seeds are killed by the animal digestion process or by composting manure. Thus, viable Palmer amaranth seed can pass through animals fed cotton-related sources and be spread onto fields through a manure application.
Check fields with "waterhemp escapes" to rule out Palmer amaranth. If Palmer amaranth is suspected, remove plants from the field immediately to help prevent additional seeds to the weed seedbank.
Source: U of M