2019 Western Iowa Palmer Amaranth Tour

September 4, 2019 7:55 AM
Blog Post

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 6th 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. This year the field was in prevented planting and was recently tilled to control weeds.  I was unable to find any Palmer among the waterhemp and marestail carcasses in the field.  An area across the road established in native perennials has had scattered Palmer amaranth plants over the years.  This year it had been converted to alfalfa and a few small patches of Palmer amaranth were present.  I didn’t find any Palmer plants along the road leading to the field which had been present in previous years.  

No Palmer amaranth was found among the carcasses of waterhemp and marestail in prevented planting field in Harrison County.


A new stop on my annual tour was a 15-acre field in a commercial area of Council Bluffs that I learned was infested with Palmer last year.  This field was also in prevented planting, but unlike the Harrison County field had a healthy infestation of Palmer amaranth.  The field appeared to have been tilled earlier in the summer, but either there was a late flush of Palmer or early-establishing plants survived the tillage.  Plants were setting seed, so even if actions were taken in the near future the seed bank would be replenished.

Less effective management of Palmer amaranth in prevented planting field in Council Bluffs.

I was on my way to Fremont County when my daughter called to say she could get off work for lunch, so I turned around at the first exit on I-29 south of Council Bluffs.  While getting back onto I-29 I spotted Palmer amaranth on the side of the entrance ramp.  This was ‘exciting’ since it was the first time I have found Palmer amaranth in Iowa without having been notified of its presence.  After lunch as I headed to Fremont County I got off the exit again to further investigate the infestation.  I was surprised to find the Palmer amaranth extending for over a half-mile along the road.  The Palmer was restricted to the area immediately adjacent to the road and didn’t extend into the area of ditch with a healthy stand of smooth brome.  

Although the source of this infestation is unknown, there is a large grain processing facility nearby that is a logical source for Palmer amaranth seed.  I was surprised at the size of the infestation since annual weeds typically don’t do very well on our roadsides. I thought maybe the roadside recently was regraded which would create a more favorable environment, but the county engineer reported the last construction at this site was in 2009.  The county engineer had been unaware of the infestation, but said the county would take immediate action. The adjacent soybean field had a lot of waterhemp, but I didn’t spot any Palmer amaranth in the field.  

Palmer amaranth on roadside in Mills County.

The Palmer amaranth in Fremont County is inside the boundaries of a town decimated by this year's flood.  There was much less Palmer  than in previous years.  It will be interesting to see if the Palmer amaranth seed was moved to new areas by floodwaters and results in a spread of the weed.

The final stop was in Page County on the grounds of a commercial ag operation that has been home of a small infestation since 2013.  As in previous years there were a few scattered plants present on the property. It is nice that the infestation isn’t getting worse, but discouraging since it wouldn’t take much effort to remove these plants and stop them from replenishing the seed bank. There was no Palmer in the adjacent soybean field.

Summary:  While I don’t gather systematic measurements of the populations at these sites, the tour allows me to see whether Palmer amaranth is increasing or decreasing in time.  It is encouraging that Palmer amaranth isn’t becoming a dominant component of the weed community and isn't expanding into adjacent areas.  The Harrison County site was by far the worst infestation of the three when they were discovered in 2013, and in the past two years I haven’t found any plants in the field where Palmer was first identified.  There have been limited numbers of plants outside of the field that could be eliminated without much effort (same as at the Page County site), but the overall progress in eradicating Palmer amaranth is encouraging.

The most disappointing finds were the poor management in Council Bluffs and the discovery of Palmer amaranth along the road in Mills County.  If we are going to stop or limit the movement of Palmer amaranth in Iowa, everyone involved in crop production needs to be observant for new infestations and prevent them from becoming permanently established. The ability to drive down the infestation in Harrison County demonstrates this weed can be beat.  The lack of a large, established Palmer amaranth seed bank in nearly all of Iowa’s crop fields makes this a winnable fight.

Previous tour blogs: