PREEMERGENCE ACTIVITY OF CHLOROACETAMIDE HERBICIDES ON A MULTIPLE HERBICIDE-RESISTANT POPULATION OF WATERHEMP (AMARANTHUS TUBERCULATUS) BY SETH ARTHUR STROM THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Crop Sciences in the Graduate College of the University of Illinois at Urbana-Champaign, 2018 Urbana, Illinois Master’s Committee: Associate Professor Aaron G. Hager, Chair Professor Dean E. Riechers, Co-Chair Professor Adam S. Davis ABSTRACT Chloroacetamide herbicides have been an integral part of preemergence (PRE) weed management programs in corn and soybean since their discovery in the 1950’s. Today they are applied either alone, or with other active ingredients in herbicide premixes. Known as ‘Old Chemistries’, their importance is due to the excellent control of annual grasses and small-seeded broadleaf weeds when applied PRE, and relatively high crop safety. Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is a small-seeded, summer annual weed species native to the Midwest. Waterhemp is dioecious with an ability to evolve resistance to herbicides from various sites-of-action. This, paired with high reproductive output, prolonged emergence, genetic diversity, and seed dormancy, has allowed waterhemp to become one of the most problematic weeds in Midwestern agronomic cropping systems. Waterhemp has displayed resistance to herbicides from six different site-of-action groups including: acetolactate synthase (ALS) inhibitors, 5-enolpyruvyl-shikimate-3-phosphate (EPSPS) inhibitors, protoporphyrinogen oxidase (PPO) inhibitors, synthetic auxins, Photosystem II inhibitors (PSII), and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. Chloroacetamide herbicides, however, have remained effective. During research on the first HPPD-resistant population of waterhemp from Mclean County, IL (MCR), significantly less- than-anticipated PRE control was reported with the chloroacetamide herbicide S-metolachlor. Similar observations were made on a separate waterhemp population from Champaign County, IL (CHR) with resistance to HPPD-, ALS-, PSII-, and PPO-inhibitors and 2,4-D. In both cases, another active ingredient from the same class, acetochlor, remained effective. With such similar observations on geographically separated waterhemp populations, field research began at the CHR location in 2016 to investigate this reoccurring anomaly. ii Chapter 1 of this thesis includes a literature review of chloroacetamide herbicides including their development, mode of action, selectivity, and the environmental interactions of a specific active ingredient, S-metolachlor. Additionally, a section reviewing waterhemp biology is included. Chapter 2 highlights field experiments conducted at the Champaign Co. site and greenhouse dose-response experiments with acetochlor and S-metolachlor. Results from field experiments demonstrated very poor control with each Group 15 herbicide except non- encapsulated acetochlor, alachlor, and pyroxasulfone, which provided 75, 67, and 56% control, respectively, 28 days after treatment (DAT). Greenhouse dose-response experiments with S- metolachlor revealed a large difference in herbicide effective dose values between populations with multiple herbicide-resistance, including resistance to HPPD-inhibitors and atrazine, and sensitive populations. A 17.9 fold difference was documented between progeny of CHR (M6) and a known sensitive population (WUS) in response to S-metolachlor 21 DAT. The difference was calculated based on the herbicide dose required to reduce the number of surviving seedlings by 50% (LD50), and S-metolachlor was not effective in controlling M6 at a field-use rate. Acetochlor, however, was effective at controlling all populations at, or below, a field-use rate. Chapter 3 describes growth chamber experiments to examine edaphic interactions as possible causes of the decreased effectiveness of Group 15 herbicides in the field, although results were inconclusive. Also included in Chapter 3 is a synopsis of experiments and their implications for future research. iii ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisors Dr. Aaron Hager and Dr. Dean Riechers for the opportunity to conduct research and pursue my Master’s degree in their programs. Being co-advised has been a great experience and each has given me different insights to the field of weed science. Coming in as a new graduate student, my research has been full of trials and tribulations and their expertise has guided me through each scenario and has helped me develop myself as an aspiring young scientist. I would also like to thank my third committee member, Dr. Adam Davis, for his statistical advice and patience with me as I continue to learn data management and statistical analysis. This by far has been one of my greatest struggles, and Dr. Davis has always been willing to share his knowledge of R programming. I would also like to thank Dr. Carolyn Butts- Wilmsmeyer for assistance with SAS programming and the statistical analysis of my data generated in the field. I am grateful for the opportunity to be a teaching assistant for Dr. Pat Tranel. Thank you for having faith in me to run the classroom when you are away and allowing me to be a part in inspiring the next generation of weed scientists. I would like to acknowledge the herbicide evaluation group: Charlie Mitsdarfer, Lisa Gonzini, and Doug Maxwell. They keep me on track, and their expertise in conducting field research has been influential in the success of my experiments. It is truly a pleasure to work with a team that cares about my research and is always eager to help in any way possible. I would also like to thank the graduate students and lab members I have been fortunate to work alongside which include: Lanae Ringler, Sarah O’Brien, Loren Goodrich, Olivia Obenland, Dr. Yousoon Baek, and Dr. Rong Ma. Thank you for each of your contributions to my research and comic relief that has made this portion of my graduate education a great experience. In addition, I iv would like to thank Brendan Alexander for his help at the field location and R programming advice, along with the many undergraduate workers that have helped in the data collection process. I understand it is not the most glorious aspect of research, but your help is truly appreciated. I would like to express my gratitude to Syngenta for funding my project and affording me many opportunities throughout my education. The opportunity to visit the Vero Beach Research Center is an experience I will never forget. I would especially like to thank Dave Thomas for his continued interest in my project and the opportunity to conduct research at the Mclean County site. In addition, I would like to thank Dr. Joe Wuerffel for his advice as I was struggling in the greenhouse, and the entire VBRC research team. It has been a pleasure to work with a company so interested in the science and producing quality products for growers around the world. Finally, I would like to thank my family. At the end of the day, family comes first and without them, I would not be here today. I would like to thank my parents Jeff and Victoria Strom for raising me to be the person I am today. Although my dad is unfortunately not here today, I know he has been watching over me the entire time and I strive to make him proud. Overall, the support and encouragement from everyone has been tremendous and as one chapter of my graduate education ends, I cannot wait for the new opportunities in the coming future. v TABLE OF CONTENTS CHAPTER 1: LITERATURE REVIEW....................................................................................1 1.1 Group 15 Herbicides: Development Timeline of Select Compounds..........................1 1.2 Group 15 Herbicides: What they control, how they control, and where they inhibit...................................................................................................................................3 1.3 Group 15 Herbicides: Selectivity, Metabolism, and Implications for Resistance............................................................................................................................5 1.4 S-metolachlor and the Environment..............................................................................7 1.5 Waterhemp Biology, Distribution, and Agronomic Importance.................................10 1.6 Research Objectives.....................................................................................................12 1.7 Literature Cited............................................................................................................15 CHAPTER 2: DIFFERENTIAL RESPONSE OF A MULTIPLE HERBICIDE- RESISTANT WATERHEMP (AMARANTHUS TUBERCULATUS) POPULATION TO CHLOROACETAMIDE HERBICIDES............................................................................25 2.1 Abstract........................................................................................................................25 2.2 Introduction..................................................................................................................26 2.3 Materials and Methods.................................................................................................29 2.4 Results and Discussion................................................................................................34 2.5 Source of Materials......................................................................................................43 2.6 Tables and Figures.......................................................................................................44