Update on Waterhemp and Palmer Amaranth in Wisconsin

Waterhemp and Palmer Amaranth in Wisconsin: an update on locations and call to report new infestations.

Mark Renz, UW Madison Associate Professor and Extension Specialist

We have been observing the continued spread of waterhemp and Palmer amaranth in Wisconsin. These species are a concern as they are more competitive, can germinate later into the season (requiring additional management), and have a high potential to develop herbicide resistance. This is a recent picture from western Wisconsin highlighting what herbicide resistant waterhemp can look like (Photo taken by Katie Wantoch).

While waterhemp has been in Wisconsin since before 1860 it has spread throughout the state with populations now in over 80% of counties (a 20% jump compared to 2009). In contrast Palmer amaranth has only been identified in fourteen locations throughout the state. See below for maps of each species of current known infestations. You will notice that some counties are shaded even though a point is not present. These are from observations did not provide a specific location.

We require active monitoring and reporting by YOU! Active monitoring has allowed us to better understand distribution of waterhemp and Palmer in Wisconsin. While our knowledge has improved greatly (over 350 known locations of waterhemp) please submit additional reports. We are most interested in new infestations in counties or parts of counties where infestations have not previous been reported. If would like to share a new observation we have several methods for doing so.

  • The easiest is to download the Great Lakes Early Detection Network App (apple or android). This app allows you to select the species you are reporting, take multiple pictures to allow us to confirm the identification, and it automatically takes GPS coordinates. Once uploaded the reports are automatically sent to us for verification. This App is free, but does take some time to learn how to operate. A brief tutorial can be found here.
  • Another option is to send an email to reportapigweed@gmail.com. Detailed instructions are available here, but in brief we are asking that you include these items in your email
    • Location of the pigweed: GPS coordinates or an address/road intersection
    • The habitat where the pigweed is growing: agricultural field (indicate what type of field, e.g. corn, soybean, etc.), home garden, roadside, or other (please describe).
    • Do you think it is herbicide resistant? if so, what herbicide has been applied.
    • Identifying pictures of the pigweed, including a picture of the whole plant, a picture of the plant stem, and a picture of the leaf and petiole (leaf stem) also are helpful to verify populations.
  • The final option is to contact a local county agent and ask for assistance.

It is our hope that this information in combination with other efforts will assist in early detection of new populations in Wisconsin and encourage management. This information will also help us to better understand what factors are driving spread. We have several videos and fatchseets that highlight how to identify waterhemp and palmer amaranth.

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