New Palmer amaranth infestations have been found in North Dakota every year starting in 2018. There are currently 20 known infestations in 14 counties in the state, with several more likely undetected or unreported. Many infestations are linked to animal feed, and typical NDSU Extension programming about control of all pigweeds does not regularly reach ranchers and animal audiences. While pigweeds should not be a weed of concern in grass pasture and rangeland, Palmer amaranth and waterhemp can cause serious issues in annual cropping fields, and anywhere manure is spread. The goal of this project is to extend Extension programming about the threat that Palmer amaranth and waterhemp pose to audiences beyond soybean farmers and agronomists.

Pigweed seeds spread through several mechanisms, including flood waters, contaminated feed and equipment, and waterfowl. While infestations may not pose serious threats to the economic bottom line of many animal operations, the presence of these weeds continually reproducing within North Dakota does increase the chances of spread to cropping fields within the state. Furthermore, manure from contaminated feed sources that are spread onto crop fields can facilitate new introductions into cropping systems, where these weeds are difficult to control.

For historical context, the Survey of Weeds in North Dakota - 2000 (ER-83) conducted by Dr. Richard Zollinger indicated that waterhemp was only found in 0.3% of surveyed fields in 2000. Waterhemp was only detected in 4 counties in that survey. Waterhemp is now found in at least 35 counties, and has become the most economically important weed for many soybean farmers. While Palmer amaranth infestations currently represent a very low percentage of cropping fields in the state, we do not want rapid expansion of this weed over the next 20 years.

This project is designed to amplify information about Palmer amaranth and waterhemp to more diverse audiences. Five important groups to engage with are North Dakota Certified Crop Advisors, North Dakota Ag Consultants, North Dakota Stockmen's Association, NDSU Animal Science Extension, and The North Dakota Weed Control Association.

This project will need to amplify information about Palmer amaranth and waterhemp to more diverse audiences. Five important groups to engage with are North Dakota Certified Crop Advisors, North Dakota Ag Consultants, North Dakota Stockmen's Association, NDSU Animal Science Extension, and The North Dakota Weed Control Association. We will use the Barnes County infestation as a case study to represent the costs associated with importing Palmer amaranth with resistance to 5 to 7 different modes of action, and the associated costs to clean up the infestation.

Beyond typical before and after surveys, we need to assess the comfort level within each group of discussing Palmer amaranth and waterhemp with their respective clientele. Did this project provide adequate supplies and programming? Is there a clear understanding of the increased costs to soybean and other rows crops if multiple herbicide-resistant Palmer amaranth and waterhemp continue to spread?

The ND CCA and ND Ag Consultants will be important groups for this project. We will want to gather an understanding of costs for a 'typical' herbicide program in different areas of the state, and will be able to compare that to herbicide programs needed for complete control of these pigweeds species. A better understanding of current input costs compared to projected input costs to control multiple herbicide-resistant Palmer amaranth and waterhemp will be an impactful message for education. Ultimately, we hope to impart a better understanding of the need for early detection, rapid response when it comes to these two weeds.

Updated December 1, 2022:

View uploaded report

Updated July 3, 2023:

View uploaded report

Palmer amaranth and waterhemp both pose serious threats to soybean production. Waterhemp is widespread in many regions in North Dakota, and we have now documented resistance to glyphosate (Group 9), ALS-inhibitors (Group 2), and PPO-inhibiting (Group 14) herbicides. Palmer amaranth is relatively new to North Dakota, and infestations remain relatively contained at this time. However, populations have been imported with resistance to five different herbicide sites of action. We have confirmed resistance to Groups 9, 2, 4 (synthetic auxins), 5 (photosystem II inhibitors), and 27 (HPPD-inhibitors). Early season research evaluations in 2022 have led to cause for concern about resistance to two additional sites of action: Group 3 (mitosis inhibitors) and 15 (VLCFA inhibitors). There is a good chance that 7-way resistant Palmer amaranth has been imported in animal feed into North Dakota. If uncontrolled, Palmer amaranth seed can spread via several mechanisms, and could become problematic if they take a foothold in crop fields.

This project will bring education about Palmer amaranth and waterhemp to different groups typically not reached by annual row crop weed science Extension activities. The goal is to continue to raise awareness and prevent spread of Palmer amaranth and waterhemp seeds into regions that do not currently have these weeds.