Palmer Amaranth

by Sam Walter, Sustainable Plant Systems major

Background/General – Palmer Amaranth (Amaranthus palmeri) is an invasive pigweed species that is quickly spreading from the Southwest U.S. to the Southeast and Midwest of the country. Palmer Amaranth can be confused with pigweed. There is no hair on the leaves or stems of the plant, the leaf pattern is ovate to diamond leaves that are widest near the base. The leaves have long petioles and the seed head is spiked.

This weed causes significant yield loss in fields of up to 90%. Female Palmer plants can produce anywhere from 100,000 – 500,000 seeds per plant. The emergence period is from April to August which gives the plant plenty of time to grow, produce seeds and cause yield loss. This plant can grow up to 3 inches a day under the correct growing conditions.

If herbicide is not applied before the plant reaches three inches in height the herbicide will be ineffective. To lower the rate of invasion of palmer amaranth it is important to know how to identify Palmer and to always be aware if there is any in the area. If buying or using equipment, know where the equipment has been and properly clean it before moving fields or areas.

Residual herbicides should be included in the program for corn and soybeans to control early emerging palmer plants. To discover palmer plants that were unaffected by the herbicide plan scout fields in mid-July. All palmer plants discovered in the field should be pulled and removed from the field. Palmer is resistant to glyphosate which causes herbicide programs to increase in rate as well as cost for farmers.

This blog post was an assignment for Societal Issues: Pesticides, Alternatives and the Environment (PLNTPTH 4597). The views expressed are those of the author and do not necessarily reflect the views of the class, Department of Plant Pathology or the instructor.

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