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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-

The introduction and spread of Palmer amaranth in Iowa undoubtedly will have a significant impact on crop production and weed management in the future.  However, since the first infestations were identified I've been intrigued by what seemed odd behavior for a plant with Palmer amaranth's reputation.

Iowa Code 317 is the section of the Iowa Code that defines the Iowa Noxious Weed Law.  Chapter 317.1 is the piece of legislation that actually defines which weeds are classified as noxious.  I like to refer to this piece of legislation as the most out-of-date law in our great state, although I will confess that I don’t know the Iowa Code well enough to know what other gems might be present in the books.

Wild parsnip is an invasive plant commonly found in roadsides, pastures, restored prairies and other areas with full sun and minimal disturbance.  It is a biennial that forms a rosette with 'celery-like leaves' (Fig. 1.) and an umbel with yellow flowers (Fig. 2).  It contains a class of chemicals (furocoumarins) that cause a skin rash known as phytophotodermatis, sometimes called parsnip burn.  The response is caused by the chemical hypersensitizing skin to UV light, thus persons only develop the rash if they remain in the sunlight following exposure.