University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Theses, Dissertations, and Student Research in Agronomy and Horticulture Department Agronomy and Horticulture Spring 4-2017 Emergence, Competition, and Management of Glyphosate-Resistant Common Ragweed (Ambrosia artemisiifolia L.) in Nebraska Soybean Ethann R. Barnes University of Nebraska-Lincoln Follow this and additional works at: http://digitalcommons.unl.edu/agronhortdiss Part of the Agricultural Science Commons, Agriculture Commons, Agronomy and Crop Sciences Commons, Botany Commons, Horticulture Commons, Other Plant Sciences Commons, and the Plant Biology Commons Barnes, Ethann R., "Emergence, Competition, and Management of Glyphosate-Resistant Common Ragweed (Ambrosia artemisiifolia L.) in Nebraska Soybean" (2017). Theses, Dissertations, and Student Research in Agronomy and Horticulture. 120. http://digitalcommons.unl.edu/agronhortdiss/120 This Article is brought to you for free and open access by the Agronomy and Horticulture Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Theses, Dissertations, and Student Research in Agronomy and Horticulture by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. EMERGENCE, COMPETITION, AND MANAGEMENT OF GLYPHOSATE- RESISTANT COMMON RAGWEED (Ambrosia artemisiifolia L.) IN NEBRASKA SOYBEAN by Ethann Robert Barnes A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Agronomy Under the Supervision of Professor Amit J. Jhala Lincoln, Nebraska May, 2017 EMERGENCE, COMPETITION, AND MANAGEMENT OF GLYPHOSATE- RESISTANT COMMON RAGWEED (Ambrosia artemisiifolia L.) IN NEBRASKA SOYBEAN Ethann R. Barnes, M.S. University of Nebraska, 2017 Advisor: Amit J. Jhala Common ragweed (Ambrosia artemisiifolia L.) is a competitive annual broadleaf weed in soybean (Glycine max) production fields throughout North America. The recent confirmation of glyphosate-resistant common ragweed in Nebraska justified the need to assess the emergence pattern and competitive ability of common ragweed in soybean and to evaluate alternative herbicide programs for effective management. The objectives of this research were to: 1) evaluate the effect of tillage and develop a predictive model for the emergence pattern of common ragweed in Nebraska; 2) model the competitive interaction between soybean and common ragweed as influenced by density and irrigation levels; 3) characterize the growth response of soybean and common ragweed in mixture and monoculture to varying irrigation levels and increasing common ragweed density; and 4) evaluate the efficacy of preplant herbicides followed by glufosinate applied alone or in tank-mixtures for control of glyphosate-resistant common ragweed in glufosinate-resistant soybean. A field study was conducted for three years to evaluate the effect of tillage timing and develop a predictive model for common ragweed emergence in Nebraska. The results of this study conclude that spring tillage does not stimulate additional emergence; therefore, tillage could be used as a component of glyphosate- resistant common ragweed management programs in Nebraska. Additionally, thermal time calculations with a temperature base of 3 C can be used to predict emergence (%). A field study was conducted to model the competitive interaction and assess the growth response of soybean and common ragweed as influenced by density and irrigation level. Soybean yield loss was not altered by irrigation amount and the leaf area ratio model at the soybean R6 growth stage best fit the data. Common ragweed densities of 1, 6, and 12 m─1 row resulted in yield losses of 61, 76, and 95% in 2015 and 25, 39, and 80% in 2016, respectively. Soybean growth was affected by common ragweed density however soybean demonstrated no plasticity. Common ragweed growth was affected by common ragweed density and irrigation. Common ragweed demonstrated plasticity by altering specific leaf area and biomass partitioning when in competition with soybean. A field study was conducted to evaluate the efficacy of glufosinate-based herbicide programs for season-long control of glyphosate-resistant common ragweed in glufosinate-resistant soybean. The results of this study conclude that glufosinate, paraquat, 2,4-D, dimethenamid-P, cloransulam-methyl, or plus chlorimuron ethyl applied preplant (PP) followed by glufosinate applied POST alone or in tank-mixture provided ≥ 84% control of glyphosate-resistant common ragweed, reduced density to ≤ 20 plants m─2, and secured ≥ 1819 kg ha─1 soybean yield. Preplant followed by POST resulted in the highest gross profit margins compared to PP alone or PRE followed by POST treatments. iv DEDICATION This thesis is dedicated to my wife and friend, Allison Barnes, for helping me realize my potential, for encouraging me to strive to be greater, and for her constant love and support. v ACKNOWLEDGEMENTS My sincere gratitude goes to my advisor, Dr. Amit Jhala, for his guidance, knowledge, and support. I would also like to acknowledge my committee members, Dr. John Lindquist, Dr. Stevan Knezevic, and Dr. Peter Sikkema for their timely advice, direction, and input into my research and courses. Thank you to Dr. Rodrigo Werle and Lowell Sandell for influencing me as an undergraduate and giving me exposure to weed science. Without the help of Jacob Nikodym, Brad Meusch, Ian Rodgers, Mason Adams, Adam Leise, Michael Fitzgerald, Murtaza Nalwala, Mitul Patel, Pedro Fiorese, and Francisco Júnior this research would have not been achievable. The additional assistance of Irvin Schleufer, Caleb Wilford, Darren Binder, Daniel Robotham, Greg Teichmeier, Daniel Simon, and Logan Loeffelholz was invaluable. I would like to recognize the friendship and guidance of my fellow lab members Dr. Debalin Sarangi, Dr. Zahoor Ganie, Parminder Chahal, Umme Kulsoom, Jake Ziggafoos, Clint Beiermann, Maxwel Oliveira, Jeremie Kouame, Don Treptow, and John Laborde. I also appreciate the support of the faculty and staff of the University of Nebraska-Lincoln Agronomy and Horticulture department. Finally, I would to thank my close friends, Jared and Molly Aden; my parents, Wyatt and Kelli Barnes; my siblings and their families, Tyrell, Sheena, and Beccah; and my in-laws, Darren and Leann Siekman, Grant Siekman, and Grace Lathrop for their moral support and encouragement throughout this program. vi Table of Contents List of Tables ..................................................................................................................... ix List of Figures .................................................................................................................... xi chapter 1: INTRODUCTION AND OBJECTIVES ........................................................ 1 Introduction ..................................................................................................................... 1 Ambrosia. .................................................................................................................... 2 Common Ragweed Biology. ....................................................................................... 2 Common Ragweed Competition. ................................................................................ 3 Objectives ....................................................................................................................... 4 Literature Cited ............................................................................................................... 7 chapter 2: CHARACTERIZATION OF COMMON RAGWEED (Ambrosia artemisiifolia L.) EMERGENCE PATTERN INFLUENCED BY TILLAGE IN NEBRASKA ..................................................................................................................... 12 Abstract ......................................................................................................................... 12 Introduction ................................................................................................................... 13 Materials and Methods .................................................................................................. 16 Field Experiments. .................................................................................................... 16 Data Collection. ........................................................................................................ 16 Tillage Effects. .......................................................................................................... 17 Model Configuration. ................................................................................................ 18 Fitting the Model....................................................................................................... 19 Model Goodness of Fit.............................................................................................. 20 Results and Discussion ................................................................................................. 20 Spring Tillage............................................................................................................ 20 Model Selection and Fit. ........................................................................................... 21 Practical Implications................................................................................................ 22 Literature Cited ............................................................................................................