Palmer amaranth requires early farmer detection to prevent spreading

UPDATE (9/26/19): Palmer amaranth was recently detected in Houston County, makings its first appearance in SE Minnesota this year. The Minnesota Department of Agriculture stresses the importance of farmers scouting their fields prior to harvest and alerting MDA if Palmer amarnath is found.

Palmer amaranth continues to be the top-of-mind invasive weed for all farmers this growing season as it finds its way into Minnesota farm operations. Early detection by farmers will continue to be the best method to prevent the spreading of this weed in 2019.

Already detected in Douglas, Jackson, Lyon, Redwood, Todd, and Yellow Medicine counties, Palmer amaranth continues to find new routes to farm fields.

Last week, the Minnesota Department of Agriculture (MDA) announced an investigation found Palmer amaranth made its way into a soybean field through cattle manure, which had come from cattle being fed sunflower seed contaminated with the weed. In October, MDA asked farmers to ensure all seed mixtures for cover crops contain a label confirming Palmer amaranth and other noxious weed seeds are not present.

Palmer amaranth can grow two to three inches per day, so early detection is crucial to prevent yield losses. If you suspect Palmer amaranth on your farm, call MDA’s Arrest the Pest (888-545-6684) to report locations. According to MDA, Palmer amaranth has the following characteristics:

  • Palmer amaranth is a summer annual that commonly reaches heights of 6- 8 feet but, can reach 10 feet or more.
  • The green leaves are smooth and arranged in an alternate pattern that grows symmetrically around the stem. The leaves are oval to diamond or triangle shaped. 
  • The leaves of some Palmer amaranth plants have a whitish V-shaped mark on them. Not all Palmer amaranth plants display this characteristic.
  • There are separate male and female plants.
  • Palmer amaranth looks similar to our native pigweeds such as tall waterhemp (A. tuberculatus), Powell’s amaranth (A. powellii) and redroot and smooth pigweeds (A. retroflexus and A. hybridus respectively). Here are some distinguishing characteristics:
    • Redroot and smooth pigweeds have fine hairs on their stems and leaves. Palmer amaranth and waterhemp do not have these hairs.
    • The petiole (stalk connecting a leaf to the stem) is longer than the length of the leaf. For tall waterhemp, the petiole will be only half the length of the leaf.
    • Seedhead spikes on female Palmer amaranth plants are much taller (up to 3 feet long) and more prickly than waterhemp or redroot and smooth pigweed spikes.
    • Genetic tests are available to confirm visual confirmation. Contact MDA at 651-201-6563 for labs offering this service.

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