Management is Key in Preventing Spread of Palmer Amaranth

It is not quite time to close the chapter on the 2015 growing season in northern Illinois. A late season discovery of Palmer amaranth in a Stephenson county field should encourage area farmers to rethink weed management plans for 2016. After notification from an area agronomist, Stephenson County Extension staff collected and delivered amaranth samples to the lab of Dr. Patrick Tranel on the University of Illinois campus. Upon delivery, the plant material was subjected to a molecular marker test. The results confirmed that the plants submitted were Palmer amaranth; the population also tested positive for the gene amplification gene present in glyphosate resistant plants.

So what does this confirmation mean to area farmers? Farmers could question how the weed arrived, and the options are many, including seed carried by harvesting and tillage equipment, as a component of crop seed or in feedstuffs, and a newer theory under investigation, carried by migrating waterfowl. Time would be better spent accepting the fact that the weed is now confirmed in northern Illinois and dedicate efforts to learn how to successfully manage the weed if found in growers fields. The elimination of small pockets or prevention of the spread of the weed is highly encouraged. Dr. Aaron Hager, Weeds Specialist at University of Illinois, has shared information on the introduction of Palmer amaranth and its spread across Illinois for several years. He stated that it is not uncommon for annual herbicide costs to at least double in areas where Palmer amaranth becomes established. There is simply no soil or foliar-applied herbicides that will provide sufficient control of Palmer amaranth throughout the entire growing season. At least three to five herbicide applications per growing season are common in areas where Palmer amaranth is well established.

What can one do at this point in the growing season? As we near the end of October and harvest nears completion, scout fields for mature pigweed type plants. If located, farmers can take initial steps to prevent the widespread (and costly) establishment of this weed. The easiest identifier for mature Palmer amaranth plants are the extended inflorescences, easily in excess of 12 inches. When the weed is present or suspected, the following are suggested:

  • We encourage farmers to not mechanically harvest mature Palmer amaranth plants with crop harvesting equipment. Physically remove the plants immediately prior to harvest and either leave the plants in the field or place in a sturdy garden bag and remove the plants from the field. Bury or burn the bags in a burn barrel as soon as possible.
  • Fields in which Palmer amaranth seeds were produced should not be tilled during the fall or following spring. Leaving the seeds near the soil surface increases the opportunities for seed predation by various granivores.
  • If the area was already harvested, mark or flag areas where Palmer amaranth plants have produced seed. These areas should be intensively scouted the following season and an aggressive Palmer amaranth management plan implemented to prevent future seed production.

University of Illinois Weed Science has published Guidelines for the Identification and Management of Palmer Amaranth in Illinois Agronomic Crops in a downloadable pdf that can be accessed at Future educational programs addressing Palmer amaranth are being coordinated with Jo Daviess, Stephenson and Winnebago County Extension offices. Printed resources about Palmer amaranth are also available at University of Illinois Extension offices in Jo Daviess, Stephenson and Winnebago Counties; call (815) 235-4125 for more information.

Source: Russ Higgins, University of Illinois Extension 

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