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This is the time of the year when late-season pigweeds (waterhemp and Palmer amaranth) poke through the soybean canopy and produce seeds. These late-season pigweeds either emerged after herbicide applications, or survived inappropriately timed or less-than-effective postemergence herbicides. Given waterhemp and Palmer amaranth’s propensity to evolve resistance to herbicides, it is also possible that the survivors are resistant to the postemergence herbicide that was used.

The first ‘official’ finding of Palmer amaranth in Iowa was August 2013 in Harrison County. Shortly thereafter the weed was identified in Muscatine, Fremont and Page County. These infestations were likely due to Palmer amaranth seed being transported on equipment/trucks involved in crop production, although the Muscatine infestation may have been associated with a swine facility.

Harrison County: Ground zero for Palmer amaranth in Iowa is a 25 acre field that had a severe Palmer amaranth infestation when the weed was first identified in 2013.  Since then populations have consistently declined - this year I was unable to find any Palmer in the field, field edges or road leading to the field. There is a small alfalfa field across the road that had a few small patches of Palmer amaranth, but a native planting that has always had some Palmer in it was clean this year.
Grade:  A-

Sensing an impending lackluster performance by the Cyclone football team, I spent the Saturday of Labor Day weekend touring several Palmer amaranth infestations in western Iowa. This is the 6^th year of this trek, the first stop is always Harrison County at the first reported Iowa infestation of Palmer amaranth. The primary field (approximately 25 acres) was dominated by Palmer amaranth in 2013 when Palmer was first identified.  Since then the population has continually declined.

The introduction of Palmer amaranth has the potential to significantly impact Iowa crop production in the future.  But as the saying goes, there’s a silver lining behind every cloud, and Palmer amaranth’s silver lining might just be the Iowa Noxious Weed Law.