2020 Western Iowa Palmer Amaranth Tour

September 7, 2020 8:19 AM
Blog Post

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-

Palmer amaranth survivors in alfalfa at Harrison Cty site.

Pottawattamie County, Site 1: In 2018 I learned of a field within Council Bluffs that is infested with Palmer amaranth (there are others that I haven't visited). The field (about 2 acres) has been in soybean the three years I visited. This year the weed control was the worst it has been since I started following it. The field had a solid stand of Amaranthus - looked to be about 2:1 mix of waterhemp and Palmer amaranth.  Most of the weeds present seemed to be plants that emerged after a late-post application of a Group 4 herbicide, but there were large plants that appeared to have survived the application due to severe bending of stems.  The only good thing I can think of is the prevalence of waterhemp - at the Harrison County site waterhemp seems to have replaced the Palmer amaranth, maybe that will happen here.
Grade: F

Applications to large plants can speed rate of resistance evolution.

Correction: Mills, not Pottawattamie, County: Last year while exiting I-29 to return back to Council Bluffs to have lunch with my daughter I spotted a few Palmers on the exit ramp.  Discovered a healthy stretch of Palmer along the road going from I-29 to a large soybean processing facility.  I notified the county about the infestation last year, but unfortunately there was no sign of improved management this year. Did not see any Palmer in the crop fields adjacent to the infested roadside. I assume the state sprayed the Palmer on the I-29 exit since the plants there were showing epinasty (and producing seed), but no sign of the county attempting control on the road. Could debate which is worse - ignoring the infestation (county) or spraying 2 ft tall Palmer with a non-lethal dose of a Group 4 herbicide (state). My error in assuming this site was in Pott County reinforces Mike Owen's assessment of me as not being a detail guy.  But it is within a mile of Pottawattamie County. Thanks for the observant reader who corrected me on my mistake. 
Grade: D 

Fremont County: This is an interesting site because the infestation is inside a small town, it was initially identified in a seed company's show plots. Over the time I've followed Palmer here the infestation has spread into non-crop areas within a couple hundred yards of the seed plots. The town was seriously affected by last year's floods, and I was curious to see if I could see evidence of movement by flooding. There were a few more escapes outside of the show plots this year than the past two years, but I was happy to see better management of Palmer in other areas where it had been largely ignored in previous years. Didn't see any sign of Palmer moving to new areas with the flooding.
Grade: B+

Page County: This site is on the grounds of a commercial ag operation.  Since 2014 there have always been a few plants among storage areas and an adjacent field.  Haven't been able to see any plants in the crop field the past couple years, but as in the past there were a few Palmer escapes scattered around the area.  Not terrible, but disappointing because it wouldn't take a lot of effort to eliminate the plants.
Grade C

Summary  As in previous years it is encouraging to see that Palmer amaranth isn't replacing waterhemp and other weeds at the locations.  However, it is disappointing that a more concerted effort isn't being taken to eradicate the weed while it is still feasible.

Previous tour blogs: