Project Profile: Pigweed Integrated Weed Management in Soybean

About Tommy Butts

I grew up outside of a small town in south central Wisconsin where agriculture became a part of my life at a very early age. I worked on small dairy farms, showed dairy cattle at the county and state fairs, and became active in 4-H and the National FFA Organization where I had the opportunity to serve as a Wisconsin State FFA Officer in 2008. I plan to obtain my Master’s Degree from the University of Wisconsin-Madison in Weed Science from the Department of Agronomy as I seek to help farmers maximize their operation’s profitability and sustainability. On Wisconsin!

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Project Title: Comparison of Integrated Weed Management Practices for the Control of Amaranthus spp. in Soybean


It is vital for Wisconsin soybean producers to maximize yields and profits in a sustainable way in order to remain competitive in a global agricultural marketplace. Integrated Weed Management (IWM) is an important tool to assist soybean growers with this purpose. IWM is a weed control strategy using a combination of multiple management tools to reduce weeds to an acceptable level while maintaining the quality of our natural resources.

Some of the most competitive annual broadleaf weed species that can adversely affect soybean production are Amaranthus species. They have prolific growth characteristics and are very competitive. These weeds have been shown to reduce soybean yields by up to eighty percent (Bensch et al., 2003). These competitive broadleaf weeds have also developed resistance to glyphosate and numerous other herbicides. Because of their competitive characteristics and prolific herbicide resistance history, using multiple methods of weed control in an IWM approach is necessary to suppress Amaranthus spp.


  1. To determine how soybean row widths and seeding rates affect the competitive ability of Amaranthus spp. in a LibertyLink soybean system and how that is influenced by using a preemergence (PRE) plus a postemergence (POST) herbicide application versus just a POST herbicide application
  2. To determine the role of light interception in soybean development and Amaranthus spp. suppression as influenced by row width, seeding rate, and herbicide strategy


Objective 1:

  • Field experiments will be conducted using a randomized complete block split-plot design to compare the whole plot factor of (2) row widths with the subplot factors of (3) seeding rates and (2) herbicide applications (PRE + POST versus POST).
  • LibertyLink soybean will be planted to alternate herbicide modes-of-action and to provide unique data compared with many previous agronomic studies using glyphosate-resistant cultivars.
  • Weeds will be counted and heights measured prior to the POST herbicide application and prior to harvest. At harvest, any mature Amaranthus spp. will be harvested, dried and weighed for biomass production, and have the seed heads threshed to determine total seed production.
  • Soybean yield and suppression of weeds will be key factors in comparison of treatments.

Objective 2:

  • Digital images will be taken weekly of each plot. Light interception will be calculated using the procedure developed by Purcell (2000).
  • Light interception values will be summed across various image dates and a best possible combination of image dates will be selected for comparisons.
  • Soybean yield, suppression of weeds, and total light interception will be key factors in comparison of treatments.


  • Bensch, C. N., Horak, M. J., Peterson, D. 2003. Interference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Science 51: 37-43.
  • Purcell, L. C. 2000. Soybean Canopy Coverage and Light Interception Measurements Using Digital Imagery. Crop Science 40: 834-837.


  • Award-winning 2014 North Central Weed Science Society meeting paper, “Light interception in soybean determined through digital imagery analysis affects soybean yield and weed suppression” [PDF]
  • 2014 North Central Weed Science Society meeting poster, “Late season weed escape survey identifies increasing numbers of herbicide-resistant Amaranthus spp. in Wisconsin” [PDF]
  • 2013 North Central Weed Science Society meeting poster, “Light Interception of Soybean as Influenced by Row Width, Seeding Rate, and Weed Competition” [PDF]

Extension Presentations

  • 2015 Wisconsin Crop Management Conference, “Herbicide-resistant pigweeds (Amaranthus spp.) are in Wisconsin, how serious is it?”

Extension Publications

  • Glyphosate resistance confirmed in two Wisconsin common waterhemp (Amaranthus rudis) populations. Thomas R. Butts and Vince M. Davis. [PDF]
  • Palmer amaranth (Amaranthus palmeri) confirmed glyphosate-resistant in Dane County, Wisconsin. Thomas R. Butts and Vince M. Davis. [PDF]
Updated January 26, 2015.