It's Labor Day weekend, that means it's time for me to see what's happening at the first three Palmer amaranth infestations in western Iowa. The infestations (Harrison, Fremont, and Page Counties) were first reported in 2013. Harrison County had two fields (approximately 50 acres) with extensive populations, whereas the other two involved scattered plants located primarily outside of production fields.
In Harrison county it was encouraging to see continuous declines in the number of Palmer amaranth escapes. I didn't find any plants during a brief jaunt into the corn field. In previous years an area filled with abandoned equipment had always contained a significant Palmer amaranth infestation. This area had been cleaned out and reseeded to perennial grass (Figure 1). While there were a few, late-season escapes producing seed, in future years the established sod should prevent future Palmer escapes. There were also a few Palmer amaranth along the road edge, but fewer than in past years. Stop one on this year's tour was encouraging, now it was time to follow the loess hills south to Fremont county (Figure 2) and determine the state of Palmer amaranth in the southwest corner of Iowa.
Unfortunately, the news in the southwest corner of the state was not as encouraging as in Harrison County. Initially I was happy to see a ditch that had been filled with Palmer in 2017 was now dominated by kochia and waterhemp. I suspect this shift was due to natural succession rather than any practices implemented by the county or landowners. The original infestation in Fremont County was found in a seed company's show plots, and the company has taken efforts (hand roguing and spraying) the past two years to eliminate these plants. There were a few escapes outside of the plots, but far fewer than in earlier years (Figure 3). Things went downhill quickly after those two observations. A sweet corn patch across the road has been a playground for Palmer the previous three years, and 2018 was no different (Figure 4). It is disheartening to think how many millions of seed are being produced in this half acre plot, and where those seeds will move to. While pondering this, the county sheriff stopped by to inquire if I was lost. While explaining what I was up to, it was clear he was wondering what kind of person doesn't have anything better to do on a three day weekend than drive around western Iowa looking for weeds.
The final stop was in Page County. At this location the Palmer is located on the grounds of an ag retailer and in an adjacent field. Because of wet conditions, I didn't venture into the corn; but the waterways in the field that harbored Palmer in previous years were clean. There have always been a few escapes around the grounds of the retailer, but it was obvious the company had made efforts to manage the population. This year those efforts weren't apparent, and there were more and larger plants scattered across the grounds than I had observed before.
In summary, if I were to rate the management efforts at the three sites, I would give a thumbs up to Harrison County, and thumbs down to the other two. Early detection and eradication should be the objective for managing new infestations of weeds. It is encouraging to see improvements in management at the Harrison County site where eradication will be most difficult due to the size of this infestation at detection. Eradication should be easier at the other sites because of their limited size, but efforts there appear to be lacking. I hope that in 20 years we don't look back and say "sure wish we would have gone after the Palmer when it was first found".