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Issue No. 16, Article 1/July 20, 2012

Palmer Amaranth Identified in West-Central Illinois

Earlier this week, a population of Palmer amaranth was identified growing in a field in Cass County, in portions where no agronomic crop was planted. A local farmer indicated that the areas with the Palmer amaranth plants were enrolled in the Conservation Reserve Program (CRP), and earlier this spring they had been seeded to provide vegetation cover. No other Palmer amaranth plants were identified in the vicinity.

How the plants became established at this location is not known. Since no other plants were observed nearby, it is possible that Palmer amaranth seeds were introduced during the seeding for vegetative cover. Whatever the mechanism of introduction, it is highly recommended that Palmer amaranth plants be removed as soon as possible--particularly before they reach reproductive development, as female plants can produce an abundant amount of seed. This weed species can be very problematic and can dramatically reduce crop yields. Its growth rate and competitive ability exceed that of most other pigweed species, including waterhemp.

Scouting for Palmer amaranth in CRP fields recently seeded to provide vegetative cover is advisable. A number of vegetative characteristics, illustrated in the accompanying photos, distinguish Palmer amaranth from waterhemp:

  • The arrangement of upper leaves on larger Palmer amaranth plants gives the plants a poinsettia-like appearance when viewed from above.
  • The leaves of Palmer amaranth are generally much larger and broader than the lanceolate leaves of waterhemp.
  • Leaves sometimes have a white (or purple) V-shaped mark on the upper leaf surface that resembles a watermark.
  • The petiole of mature leaves is very long, often 2 to 3 times the length of the leaf.

The poinsettia-like appearance of Palmer amaranth.

Watermark or V-shaped variegation on the leaves of Palmer amaranth.

The long leaf petiole of Palmer amaranth.

Palmer amaranth's large, broad leaf.

Figure 1 illustrates a side-by-side comparison of Palmer amaranth and waterhemp. If you would like assistance identifying plants you suspect of being Palmer amaranth, please let us know.

Figure 1. To distinguish Palmer amaranth from waterhemp, evaluate the characteristics detailed above.

--Aaron Hager

Aaron Hager

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