Male Palmer Amaranth Plants

Jul 31, 2015

By Rich Zollinger

Extension Weed Specialist

In the last issue of the NDSU Crop and Pest Report (#12) I included information on Palmer amaranth. In the article I indicated the following:

Below are reasons why it is being called “Satan” and why growers should quickly destroy any plants found.

#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 are small and generally non-competitive.

My kind colleague, Dr. Dallas Peterson at Kansas State University responded that the information is not entirely accurate. His corrections are:

“I would disagree on your point about male plants being small and noncompetitive. Although male plants senesce earlier than females and typically don't grow as large late in the season, they still can be fairly large and competitive through much of the season. Attached is a picture (Photo 1) I just took with female and male Palmer amaranth side beside where both genders are well over 6 ft. tall (much taller than most wimpy ND weeds). Once the males 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 the females that can get to be 3 to 4 inches in diameter. A thick stand of Palmer amaranth will basically result in 100% soybean yield loss because of competition and harvest difficulties (Photo 2).

Source: ndsu.edu

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