Don’t Give Up The Fight

Teresa Olson
By Teresa Olson April 18, 2017 08:58


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It’s been almost 3 years to the day that I wrote about the “Careless Weed” (  It was at that time that Bob Hartzler  and Mike Owen, weed specialists from Iowa State University stated that Palmer amaranth was just moving into their state.  Last year conservation seedings contaminated with Palmer amaranth seeds joined fields contaminated by traditional farming practices to the point where 49 of Iowa’s 99 counties now have confirmed Palmer amaranth infestations.

This is no laughing matter.  As a weed native to most of the southern half of North America, it has now been reported in Minnesota, South Dakota, Michigan and Wisconsin.  It’s not in North Dakota – YET, and Montana is afraid it may be headed in their direction.  As you may well know, Palmer amaranth has caused severe yield losses up to 91% in corn and 79% in soybeans.  Bill Johnson, Purdue University Extension weed specialist says, “It’s the only weed I’ve seen that can drive a farmer out of business.”

Considering this weed has become resistant to certain herbicides, actions are varied.  In the Midwest, it emerges from May to September which forces farmers to manage it throughout the year.  It can hybridize with other pigweeds, and its reproductive habits allow it to readily adapt to new environments.  Fortunately at this point Palmer amaranth has not yet adapted to conditions in more northern states.  Bob Hartzler states that it typically takes weeds 20 years to adapt to a new environment, so it’s easier to manage it now than it will be in 15 to 20 years.


I read through several sources and wanted to recap some information that might provide some insight when battling this weed:

  • Because 20-25 degree soil temperature flucuations (not the sun) initiate germination in these seeds, crop leaf canopies and field residue that keep soil temps fairly constant can effectively reduce Palmer amaranth emergence.
  • Other cultural practices to decrease resistance weed seed survival include proper composting – raising compost pile temperatures above 160 degrees to sterilize weed seeds.
  • Possibly using deep tillage (4-6 inches deep so there is no germination) once every three or four years for dense weed populations and using intense crop rotation and herbicide rotation.  This may erase all the benefits of reduced or no-till , but a Missouri University found that no-till left 95% of pigweed seeds on the surface versus 18% after deep tillage.
  • Palmer amaranth can be toxic to livestock animals due to the presence of nitrates in the leaves.
  • Report suspected infestations for confirmation, and avoid entering the infested area.  If you must enter, always clean vehicles, equipment and clothing prior to exiting the area, and be certain machinery is clean when moved from field to field.
  • For conservation plantings, use only local reputable seed sources, limit soil disturbance and utilize cover crops to prevent and help suppress weed infestations.
  • Purchase certified seed if possible as it has been field inspected for weeds and other contaminates.
  • Read seed labels carefully before purchasing.  If a dealer won’t provide a label or “Laboratory Report of Analysis” for your mix, consider other vendors.
  • Scout fields for several years and use appropriate weed control.
  • Don’t take manure from an animal operation originating from mid-South states that has used cottonseed as feed.
  • Palmer amaranth-infested hay has also come from Kansas and Oklahoma.
  • Cleaning up and blowing out combines after harvesting infested fields can prevent the spread of Palmer amaranth.
  • In CRP and pollinator mixes: Mowing is not always effective, but if you do mow, do it regularly at a 6-8 inch height.  Some Palmer amaranth will survive, but this should reduce seed production in the field.
  • Hand-roguing (pulling female plants by hand to prevent cross-pollination) is more difficult, but possible for the CRP and pollinator mixes.
  • Narrow soybean rows (from 10-20″) enable the soybeans to canopy quickly, preventing sunlight from getting to the weeds.

The bottom line to your fight against this weed?  Don’t give up.  Learn to recognize Palmer amaranth, and take immediate steps to prevent its spread.  Your livelihood depends on it!

-Terry Olson, Titan Outlet Store Team




Teresa Olson
By Teresa Olson April 18, 2017 08:58
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