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OSU Extension

College of Food, Agricultural, and Environmental Sciences

CFAES

Wayne County

August 21, 2015 - 2:50pm -- Anonymous

Recently palmer amaranth was confirmed in two separate field locations in Wayne County.  Palmer amaranth is an aggressive, invasive weed.  This is a weed species that is making its way northward from our southern states where it is a major problem in cotton and soybean fields.  Virtually all palmer amaranth populations are known to have partial or complete resistance to glyphosate.   In one of the Wayne County sites it was this resistance to a glyphosate application that alerted the landowner to the presence of the weed.  Most populations of palmer amaranth are also resistant to the ALS herbicides; for example First Rate, Classic and Canopy.  In southern states there have been numerous instances where soybean fields have had to be destroyed and tilled under because palmer amaranth over took the field and there was no herbicide control option available.  Extension weed specialists in some of those southern states talk about soybean producers now spending three to four times more on weed control since palmer amaranth has become more common.  There are stories of growers spending $100/acre and more to hire labor to hand pull palmer amaranth from infested fields.  Palmer amaranth is capable of taking over fields because an individual plant can produce up to 500,000 seeds. 

Some identification characteristics of palmer amaranth include:

  • Rapid growth rate: often between 1 to 3 inches per day.  Mature plants can reach 7 feet in height under normal growing conditions.
  • An extended petiole.  The petiole is the stem that connects the leaf blade to the main stalk of the plant.  On palmer amaranth the petiole will be at least as long as the leaf blade and commonly extends beyond the leaf blade.
  • A long seed head.  On palmer amaranth, the seed head will be more than a foot in length and is usually at least 18 inches in length but may reach 24-30 inches.

At this time landowners, crop growers, custom sprayers, custom harvesters, crop consultants or anyone who works with agronomic crops should be aware of the threat of large scale palmer amaranth infestations in the county.  We want to limit the spread of this weed and eradicate it wherever possible.  If a weed is found that is suspected to be palmer amaranth, submit a sample or photos of the plant to the Wayne County Extension office.  If a positive palmer amaranth identification and confirmation is made, the following management practices are suggested:

  • Hand pull, remove from the field and destroy the weeds as soon as possible.   Once viable seed is produced, hand pulling is no longer recommended as this can serve to spread the seed.
  • If hand pulling is not possible and the palmer amaranth weeds are located where they can be mowed or clipped off, then do that.  This practice should also be done before weed seeds are viable.
  • If neither hand-pulling nor clipping is possible then make sure that crop field where the weed is present is harvested last and any harvest equipment is thoroughly cleaned before moving into a field where palmer amaranth is not present.
  • Plowing after harvest to bury seed more than one inch deep could provide some control on fields where there is little to no erosion potential.
  • Rotate from soybeans into corn where there are more herbicide options to control palmer amaranth.

More information about palmer amaranth including identification characteristics, biology and life-cycle of the weed, control options and photos of the weed are available on the Wayne County Extension web site at: http://go.osu.edu/agwayne or contact the office at 330-264-8722.