Palmer amaranth is now a prohibited noxious weed seed in Wisconsin, but what does it look like?

by Rodrigo Werle (UW-Madison Extension Cropping Systems Weed Scientist)

Under a new emergency rule, Palmer amaranth has been labeled as a prohibited noxious weed seed in Wisconsin. Given Palmer amaranth’s aggressive nature, this is a worthwhile and necessary attempt to keep this troublesome weed species out of the state. For more details, see DATCP article: “Keep an Eye Out for Palmer Amaranth, DATCP Cautions”.

Palmer amaranth’s late and extended emergence window throughout the growing season and vigorous growth rate (up to 2 inches per day under ideal conditions) make control in row crops very difficult. Palmer amaranth is a major weed problem in the US Mid-South and parts of the Midwest. According to University of Wisconsin-Madison Weed Scientists, Palmer amaranth has been reported in 6 Wisconsin counties thus far (see map below).

"Palmer distribution"

One way that Palmer amaranth seeds may get introduced to a new region is via contaminated conservation or pollinator seed mixes. Thus, purchase seed mixes free of amaranth species. Moreover, be on the lookout for Palmer amaranth in areas where these seeds are planted. Equipment moving from Palmer amaranth infested areas can also transport seeds; thus, thoroughly clean equipment coming from regions where the species is present.

One of the first steps to prevent further spread of a noxious weed species, is to properly recognize it. Below I have images that may help stakeholders identify this troublesome weed and differentiate it from other common Pigweed species.

The key identifying characteristics of Palmer amaranth are:

  • lack of hairs on leaves and stems
  • long petiole (structure that connects the leaf blade to the stem; the petiole of a Palmer amaranth leaf is typically as long or longer than the leaf blade itself)
  • female plants have long and prickly seedheads

"Pigweed family"

"Palmer amaranth"


"redroot pigweed"

Female Palmer amaranth plant growing in a corn field in West-Central Nebraska (note the plant height and seedheads [long and prickly]):
"Palmer amaranth corn"

The YouTube video by UW-Madison Extension Weed Specialist Dr. Mark Renz is also a great resource to help stakeholders identify and differentiate Palmer amaranth from other Pigweed species: “Identifying Palmer amaranth and Waterhemp in Wisconsin using vegetative characteristics”

Contact your local University of Wisconsin County Ag Extension Agent if you need assistance to identify this species.

Let’s all work together to keep Wisconsin Palmer-FREE!