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OSU Extension

College of Food, Agricultural, and Environmental Sciences

July 19, 2016 - 8:35pm -- lewandowski.11@...

          Last year new infestations of palmer amaranth were found in Wayne and Mahoning counties.  This is not a problem that goes away when it is ignored.  There is potential for this weed to explode across the county and greatly increase the cost of soybean production as well as causing yield loss.  Once palmer amaranth is present, the situation is serious, as this weed produces up to 500,000 seeds per plant.  It can grow up to three inches per day.  Most populations are resistant to glyphosate and ALS inhibitors (site 2 mode of action).

           Based on the history of the fields where we found this weed last August, it is suspected that palmer amaranth may be more widespread in the county than just a couple of fields.  Now is the time of year that growers should be scouting their soybean fields, to identify possible palmer amaranth infestations.  Recently Mahoning County ag educator Eric Barrett sent out a palmer amaranth advisory to growers and I think that advisory is valid to repeat here.


  • Palmer amaranth plants are already ahead of the crop.   Once palmer amaranth plants reach 5 inches or greater in height there is no effective herbicide option.
  • Plants without mature seed (black) should be pulled out (uprooted) or cut off just below soil and removed from field, and then burned or buried at least a foot deep or composted. Plants with mature seed should be bagged and removed from field.
  • If the Palmer amaranth population is too dense to remove from the field, some decisions need to be made about whether or how to harvest.  Harvesting through patches or infested fields will result in further spread throughout the field and also contamination of the combine with Palmer amaranth seed that can then be dispersed in other fields.  So consider:

1) not harvesting areas of the field infested with Palmer amaranth, and

2) harvesting the infested field(s) after all other fields have been harvested, and cleaning the combine thoroughly before further use.  This also applies to any Palmer amaranth infestations that are discovered while harvesting. NOTE: The stem of this plant can be over 3” in diameter at the soil surface.


  • Develop a scouting strategy for your farm. Help your neighbors identify this plant.
  • Use these photos and details to watch for this as you drive through the county:
  • Get help with identification if in doubt.  Call me at the Wayne County Extension office (330-264-8722) or connect with others who can assist in identification.

Read more about the status of Palmer Amaranth in Ohio here: