Waterhemp management in soybean was challenge for several Wisconsin farmers in 2019. The use of PRE-emergence herbicides is a foundation for effective waterhemp control; however, results from our “2018 weed management survey” indicated that the use of a single POST herbicide application is still a common weed control strategy for several farmers in the state. Furthermore, recent research by the UW-Madison Cropping Systems Weed Science Lab revealed that waterhemp resistance to glyphosate (EPSPS; Group 9) and imazethapyr (ALS; Group 2) is widespread across corn and soybean fields in Wisconsin, limiting effective POST herbicide control options, particularly in soybean (see “Wisconsin Waterhemp Herbicide Resistance Project – 2019 Update” for an in depth look at those results).
Starting in 2018 (“2018 UW-Waterhemp Challenge: Comparison of Soil Residual Soybean Herbicides”), and replicated in 2019, a study was conducted to evaluate and demonstrate the effectiveness of multiple PRE-emergence soybean herbicides. This was a joint effort between the UW-Madison Nutrient and Pest Management Program (NPM; Dan Smith and Richard Proost) and the UW-Madison Cropping Systems Weed Science team. The study was conducted both years at UW Lancaster Ag Research Station, in Lancaster, WI (Grant Co; Southwest WI) in fields naturally infested with waterhemp. Treatments consisted of PRE-emergence soybean herbicides with one, two, or three different active ingredient(s) and/or site(s) of action (SOA). Herbicide rates tested in this study were selected based on recommendations for a typical WI Silt Loam soil. Herbicides were sprayed within 3 days after soybean planting and visual efficacy data collected at 25 and 50 days after treatment.
When selecting a PRE-herbicide program, it is important to balance efficacy and product cost. Always consider soil characteristics, geographic restrictions and crop rotation when determining which products and rates to use in your PRE-emergence herbicide program. The residual activity of a PRE-emergence herbicide is dependent on the rate applied; cutting rates is not a recommended strategy when attempting to manage troublesome weeds like waterhemp. Always read, understand, and follow the pesticide label.
Stay tuned for additional research updates related to control of waterhemp and other troublesome weeds in Wisconsin as well summer plot tour opportunities in 2020!
Take-Home from the “Residual Control of Waterhemp with PRE-emergence Herbicides in Soybean” Publication:
- Due to its genetic variability, wide emergence window, vigorous growth potential, and prolific seed production, waterhemp has become a troublesome weed in soybean cropping systems.
- Wisconsin research summarized herein demonstrates the effectiveness of incorporating pre-emergence herbicides into waterhemp management programs.
- Effective herbicide programs should be determined on a field to field basis taking into consideration soil properties, geographic restrictions, subsequent crop(s), and soil seedbank weed species composition, pressure, and presence of herbicide resistance.
- Sustainable management of herbicide-resistant waterhemp populations requires a holistic integrated approach incorporating cultural and/or mechanical practices alongside chemical herbicide programs.
- Remember, don’t let them seed. No seed, no weed!
Acknowledgements: We would like to thank Mimi Broeske, UW-NPM Senior Editor, for developing the publication layout. Members of the UW-Madison Cropping Systems Weed Science Lab helped with study establishment and data collection. Thanks to Doug Wiedenbeck and the UW Lancaster Ag Research Station staff for their support. Thanks to industry colleagues who helped in developing the rate structure for this study. This study was partially funded by the Wisconsin Soybean Marketing Board.
Authors: Nicholas Arneson (UW-Madison Weed Science Outreach Specialist), Dan Smith (UW NPM Southwest Wisconsin Regional Specialist), Ryan Dewerff (UW-Madison Weed Science Research Specialist), Maxwel Coura Oliveira (UW-Madison (UW-Madison Weed Science Postdoctoral Research Associate), and Rodrigo Werle (UW-Madison Extension Cropping Systems Weed Scientist).