Iowa: Palmer Pigweed – Add Osceola County to the Map – Increased Vigilance Needed

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A farmer in Osceola County recently found a single Palmer amaranth in a soybean field. He removed and burned the offending plant. This brings the ‘official’ ISU count of infested counties to 50. As we’ve stressed before, Palmer amaranth is likely in many more counties than reported to us.

Herbicide Resistance Info


The finding of this plant reinforces the importance of increased vigilance to find new infestations of Palmer amaranth. Palmer amaranth is now widely established across the state, so it’s likely new infestations will randomly appear in new fields at an increasing frequency. 

While pigweeds do not have inherent dispersal mechanisms, the abundant small seeds are easily transported by farming operations and wildlife. Every field in the state is at risk of being invaded.  

A new infestation in the opposite corner of Fremont county than the initial detection was also found this week.

Late summer is probably the simplest time to locate Palmer amaranth in soybean fields, although it is preferable to identify them earlier in the season. The terminal inflorescences of Palmer amaranth are typically thicker and longer than those of waterhemp, thus plants can be identified from a considerable distance if a person is observant. 

While it is likely some seed may have already shed, removing female plants at this time can minimize future populations and enhance the likelihood of eradicating the weed from individual fields.  As Smoky said, “Only you can prevent the spread of Palmer!”

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Long inflorescences on Palmer amaranth above soybean canopy.