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Evaluation of Tolpyralate for Weed Management in Field Corn (Zea Mays L.)

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Evaluation of Tolpyralate for Weed Management in Field Corn (Zea Mays L.) Evaluation of Tolpyralate for Weed Management in Field Corn (Zea mays L.) By: Brendan A. Metzger A Thesis Presented to The University of Guelph In partial fulfilment of requirements For the degree of Master of Science In Plant Agriculture Guelph, Ontario, Canada © Brendan A. Metzger, January, 2019 ABSTRACT EVALUATION OF TOLPYRALATE FOR WEED MANAGEMENT IN FIELD CORN (Zea mays L.) Brendan A. Metzger Advisors: University of Guelph, 2019 Dr. P. H. Sikkema Dr. D. E. Robinson Twenty-seven field experiments were conducted from 2015-2018 at nine locations to evaluate tolpyralate, a new pyrazolone 4-hydroxyphenyl-pyruvate dioxygenase inhibitor, for weed management in corn. The biologically-effective dose of tolpyralate and tolpyralate + atrazine was established in eight common annual weed species, and separately in multiple herbicide-resistant (MR) Canada fleabane and waterhemp biotypes. Co-application of tolpyralate with atrazine improved weed control; tolpyralate + atrazine at label rates provided similar or improved control of eight common weed species, MR Canada fleabane and MR waterhemp compared to industry standards. Four weed species were controlled equally regardless of POST application timing and two species were controlled with tolpyralate + atrazine applied pre- emergence; annual grass control declined with delayed applications. Corn was at greatest risk of injury with tolpyralate + atrazine applied at V1 or V3, and at 2X rates. Injury was influenced by environmental variables, but did not translate to grain yield loss. Acknowledgements As my time as a student comes to a close, I would like to thank all those who have played a role in making the past two years not only successful but truly enjoyable. To my advisors Dr.’s Peter Sikkema and Darren Robinson, I can’t express how much I appreciate your guidance, support, advice and encouragement. Despite extremely full schedules and extensive field programs, you consistently bend over backwards to make your graduate students and their projects a priority, and go out of your way to make them feel welcome and valued as members of the team. You’ve taught me to be a better researcher, writer and presenter, but I’ve also learned what it means to be an outstanding leader. Thank you also to Dr.’s Dave Hooker and Alan Raeder for serving on my advisory committee, and a special thanks to Alan for making numerous trips north for meetings and tours. From writing to research tours, I greatly appreciate the time, effort and perspective both of you contributed to my project; the quality of this research is improved thanks to your involvement. A sincere thank you to Dr. Nader Soltani, for your tireless efforts in getting manuscripts fit for publication, your dedication to the program, and for always being the graduate students’ number one fan. Field research is truly a group effort, and I owe a huge thank you to everyone who helped with this project at ground level. To my fellow graduate students: Andrea Smith, Lauren Benoit, Brittany Hedges, Elizabeth Buck, Jessica Quinn and Nicole Langdon, thank you doesn’t begin to describe my appreciation for all of the help, comradery, moral support and comic relief throughout the past two years. Thank you all for welcoming a male presence into the crew; I couldn’t have asked for a better group of people to share a small, windowless office with. To Todd Cowan, Christy Shropshire, Chris Kramer and Lynette Brown, thank you for the time each of you dedicate to making sure graduate students are successful, while still managing busy field programs of your own. I greatly appreciate your help in planning, training and trial execution, and also the independence that you grant graduate students to truly manage their research. A special thanks to Christy for your patience in working through statistics with me and all of the graduate students. To all of the Sikkema summer students at Ridgetown and at Huron, a big thanks to each of you for your help with some of the most gruelling aspects of this project. Whether it was staking, hoeing or colossal weed harvests, I appreciate the sweat equity that each of you have put into this research project and many others. Thank you also to Dr. Michelle Edwards for all of your assistance with statistical analysis. You go above and beyond for all of the graduate students; we and the entire OAC are lucky to have you. Thank you to ISK Biosciences Corporation, Grain Farmers of Ontario, and the Growing Forward 2 program for their financial contributions that made this project possible, as well as landowners who generously allowed the use of their land. Finally, I would like to thank my friends and family members for their encouragement and support throughout my studies. I’m privileged to have such a solid group of supportive people in my life. iii Table of Contents ABSTRACT .................................................................................................................................................. ii Acknowledgements ...................................................................................................................................... iii Table of Contents ......................................................................................................................................... iv List of Tables ............................................................................................................................................... ix List of Figures ............................................................................................................................................ xiv Chapter 1: Literature Review .................................................................................................................... 1 Section I - Weed Control in Corn ............................................................................................................. 1 1.1 Corn Yield Loss Due to Weed Interference .................................................................................... 1 1.2 Effects of Weed Competition in Corn ............................................................................................. 2 1.3 Development of the Critical Weed-Free Period .............................................................................. 3 1.4 Factors Influencing the Critical Weed-Free Period in Corn ........................................................... 4 1.5 Evolution of Weed Management Strategies .................................................................................... 6 1.6 Herbicide-Resistant Crops .............................................................................................................. 6 1.7 Herbicide Management Strategies and Two-Pass Weed Control ................................................... 7 1.8 No-till Farming and Implications for Herbicide Stewardship ......................................................... 9 Section II – HPPD Inhibiting Herbicides and Tolpyralate...................................................................... 10 2.1 HPPD Mode of Action .................................................................................................................. 10 2.2 HPPD-Inhibitors: Discovery and Designations ............................................................................ 11 2.3 HPPD-Inhibitors: Uptake and Translocation ................................................................................ 12 2.4 HPPD Inhibitors: Selectivity ......................................................................................................... 13 2.5 Photosystem II Inhibitors: Interactions and Synergy .................................................................... 14 2.6 Tolpyralate: Discovery and Development .................................................................................... 15 2.7 Tolpyralate: Application Timing, Activity and Control Spectrum ............................................... 16 2.8 Tolpyralate: Comparisons to Industry Standards .......................................................................... 17 2.9 Tolpyralate: Crop Tolerance and Re-Cropping Restrictions......................................................... 19 Section III - Effect of Weed Size on Herbicide Efficacy ........................................................................ 20 3.1 Effects of Delaying Weed Control ................................................................................................ 20 3.2 Contact Herbicides ........................................................................................................................ 21 3.3 Systemic Herbicides: ALS-Inhibitors, ACCase-Inhibitors and Synthetic Auxins ........................ 23 3.4 Systemic Herbicides: Glyphosate ................................................................................................. 24 3.5 Factors Affecting Herbicide Efficacy ........................................................................................... 25 iv 3.6 Overcoming the Influence of Weed Size on Herbicide Efficacy .................................................. 26 Section IV - Glyphosate-Resistant Weeds and Canada Fleabane (Conyza canadensis (L.) Cronq.) ...... 29 4.1 Glyphosate: Discovery and Development ..................................................................................... 29 4.2 Glyphosate: Mode of Action ......................................................................................................... 29 4.3 Glyphosate: Application, Uptake and
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