Crop & Pest Report


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Vigilent Watch for Palmer Amaranth (06/30/16)

To date, Palmer amaranth has not been documented in North Dakota. We want to keep it that way.

Vigilent Watch for Palmer Amaranth

To date, Palmer amaranth has not been documented in North Dakota. We want to keep it that way. There has been a concerted education program in North Dakota from academia and industry for correct identification of Palmer amaranth. For review below are some reasons why we don’t want to let it get started and why growers should quickly destroy any plants if found.

1. Biotypes of this weed are resistant to one or more of the following herbicide site of action groups: ALS (2), atrazine (5), glyphosate (9), and HPPD inhibitor (27) herbicides, leaving very few herbicide options available for management.

2. One of the fastest weed growth rates known - >2 inches/day.      

3. Long emergence pattern from mid-May through August.

4. Can exploit even slight canopy openings.

5. Produces from 1 to 1.8 million seeds/plant.

6. Seed is short-lived and only 2% of seed is viable after 6 years but the sheer number of seeds produced by a female plant makes eradication difficult once established.

7. Female plants can grow to more than 10 feet tall with a 5-6 inch stem girth and seed heads more than 1 foot in length. Male plants senesce earlier than female plants and typically don't grow as large late in the season but can be fairly large and competitive through much of the season. Once male plants are done shedding pollen they will quit growing, whereas the females will continue to growth in height and stem girth. Male stems usually don't get more than about 1 inch in diameter vs female stems can get 3 to 4 inches in diameter (Photo 1).

8. Can cause 78% yield loss in soybean, 91% in corn. A thick stand of Palmer amaranth will basically result in 100% soybean yield loss because of competition and harvest difficulties (Photo 2).

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Identification of Palmer amaranth in the seedling stages is very difficult as redroot pigweed, Powell amaranth, and waterhemp may have many similar features. See next page for excellent photos from websites that show Palmer amaranth plants for identification (Photos 3 & 4).

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Rich Zollinger

Extension Weed Specialist


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