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Background

  • Glyphosate-resistant waterhemp was first identified in Missouri in 2005 and subsequently has been identified in Illinois and several other states.
  • Given the heavy reliance on glyphosate for weed management in both corn and soybean, glyphosate-resistant waterhemp is driving changes in the approach to weed management in Illinois.
  • Further exacerbating this problem is the increasing prevalence of resistance to PPO-inhibiting herbicides (e.g., the diphenylethers) in waterhemp, sometimes “stacked” with glyphosate resistance.

Objectives

  • A survey was conducted of grower-submitted waterhemp samples from across Illinois to evaluate the prevalence of glyphosate- and PPO-resistant populations.
  • Objectives of this study were to:
    • Increase awareness among farmers that glyphosate-resistant waterhemp is becoming prevalent in Illinois.
    • Confirm the existence of glyphosate-resistant waterhemp in grower fields and the need for alternative waterhemp management strategies.

Study Description

  • Samples of waterhemp suspected to be resistant to glyphosate were solicited from Illinois growers.
  • Over 1,200 plant samples were received from 252 Illinois fields from 2010-2014.
  • DNA was extracted from each sample and used in molecular assays to test for resistance to glyphosate and PPO-inhibiting herbicides.
    • For glyphosate resistance, the molecular assay detects amplification of the EPSPS gene, which encodes the glyphosate target site.
    • For resistance to PPO inhibitors, the molecular assay is based on a specific mutation that has been found in the PPX gene, which encodes the target site of these herbicides.

Results

  • This study determined that waterhemp populations that are resistant to PPO inhibitors and to glyphosate are common across the state of Illinois.
  • Samples from 94 fields evaluated in 2014 showed that nearly half of the fields had both glyphosate and PPO-inhibitor resistance present in the waterhemp population (Figure 1).
  • Glyphosate-resistant waterhemp increased in prevalence across the state during the study period (Figure 2).
  • See the following: Take Control of Weeds With Enlist One® and Liberty® Herbicides.

Percentage of fields with no resistance - resistance to glyphosate - resistance to PPO-inhibiting herbicides - or resistance to both herbicides.

Figure 1. Percentage of fields with no resistance, resistance to glyphosate, resistance to PPO-inhibiting herbicides, or resistance to both herbicides.

Illinois counties in which glyphosate-resistant waterhemp has been identified based on grower-submitted samples 2011-2014.

Figure 2. Counties in which glyphosate-resistant waterhemp has been identified based on grower-submitted samples 2011-2014.


Research conducted by Dr. Pat Tranel, University of Illinois, as a part of the Pioneer Crop Management Research Awards (CMRA) Program. This program provides funds for agronomic and precision farming studies by university and USDA cooperators throughout North America. The awards extend for up to four years and address crop management information needs of Pioneer agronomists, Pioneer sales professionals and customers. The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation.