AMINOCYCLOPYRACHLOR EFFICACY ON NATIVE FORBS, AND SOIL SEEDBANK CHANGE 15 YEARS FOLLOWING RELEASE OF LEAFY SPURGE (EUPHORBIA ESULA L.) BIOLOGICAL CONTROL AGENTS A Thesis Submitted to the Graduate Faculty of the North Dakota State University of Agriculture and Applied Science By Blake Marie Thilmony In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Major Program: Plant Sciences April 2016 Fargo, North Dakota North Dakota State University Graduate School Title Aminocyclopyrachlor Efficacy on Native Forbs, and Soil Seedbank Change 15 Years Following Release of Leafy Spurge (Euphorbia esula L.) Biological Control Agents By Blake Marie Thilmony The Supervisory Committee certifies that this disquisition complies with North Dakota State University’s regulations and meets the accepted standards for the degree of MASTER OF SCIENCE SUPERVISORY COMMITTEE: Dr. Rodney G. Lym Chair Dr. Gary Clambey Dr. Edward DeKeyser Dr. Greta Gramig Dr. James Hammond Approved: April 26, 2016 Dr. Richard Horsley Date Department Chair ABSTRACT Native prairie response to aminocyclopyrachlor (AMCP) was evaluated in the Northern Great Plains. AMCP altered plant communities and reduced foliar cover of introduced, high seral, and low seral forb species. After treatment, high and low seral monocots increased at both sites due to reduced competition from susceptible forbs. AMCP reduced richness, evenness, and diversity. Aphthona spp. were released in the Little Missouri National Grasslands in North Dakota in 1999 for leafy spurge biological control. Soil seedbank composition was sampled from two ecological sites to evaluate changes in the plant community. By 2014, leafy spurge abundance decreased 92% on average. Subsequently, Kentucky bluegrass increased, but has also been deterred by a slow reintroduction of native species. High seral forb species richness has doubled in both ecological sites since 1999. Aphthona spp. successfully controlled leafy spurge for over 15 yr without any additional control methods or costs to land managers. iii ACKNOWLEDGEMENTS First off, I would like to thank my advisor, Dr. Rodney G. Lym, for providing me with this opportunity and granting me this assistantship. You have always accepted nothing less than the best from me which has allowed me to succeed and improve in so many ways while working towards my Masters Degree. Next, I would like to recognize my Graduate Committee. Thank you to Dr. James Hammond, you truly simplified the analysis and statistics process for me. To Dr. Edward DeKeyser, I would not have been able to identify all of the species in either of my studies without your assistance, patience, and expertise. To Dr. Gary Clambey, you were instrumental to my education and my interest in ecology was emphasized by how much I enjoyed your classes. To Dr. Greta Gramig, you provided me with extremely valuable insight and advice, and your door was always open to me whenever needed. I will forever be grateful for the time and effort that each of you has given me and fully appreciate your input towards my education and career. A special thanks to Dr. Jack Norland, my undergraduate advisor, for always encouraging me and recognizing my efforts, and for continuing to provide me with advice and assistance during my graduate studies. Many thanks to Kathy Christianson for your expertise and assistance in the field and greenhouse. I must also thank all my fellow graduate students and colleagues at North Dakota State University for their friendship throughout my graduate studies. Morgan Hanson and Amanda Crook, you two have become great friends of mine and I am so thankful for the chance to have gotten to know each of you and for the numerous times you have helped me along the way. Travis Carter, working alongside you has truly been a pleasure. iv I would like to thank my parents, Steve and Becky Thilmony, and my brother and nephew, Adren Pierce and Finn Patterson, for always supporting my endeavors and making sacrifices for my benefit. Lastly, I need to thank Cole Larsen for always being there for me. You have supported and motivated me in so many ways and I could not have made it through graduate school without you. I can’t fully express the level of appreciation and gratitude I have for all of you for everything that you have done for me. Thank you. v TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii ACKNOWLEDGEMENTS ........................................................................................................... iv LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES ....................................................................................................................... ix OBJECTIVES ................................................................................................................................. 1 INTRODUCTION .......................................................................................................................... 2 AMCP Efficacy Study ................................................................................................................ 2 Seedbank Succession Study ........................................................................................................ 3 LITERATURE REVIEW ............................................................................................................... 4 AMCP Efficacy Study ................................................................................................................ 4 Distribution and Geographic Variation ................................................................................... 4 Pleistocene History ................................................................................................................. 5 Climate .................................................................................................................................... 6 Prairie Pothole Region (PPR) ................................................................................................. 8 Native Prairie Plant Communities........................................................................................... 9 Nontarget Effects of Chemical Control ................................................................................ 10 Aminocyclopyrachlor ........................................................................................................... 13 Seedbank Succession Study ...................................................................................................... 14 History ................................................................................................................................... 14 Biology .................................................................................................................................. 14 Economic Impact .................................................................................................................. 15 Control Methods ................................................................................................................... 16 Soil Seedbank ........................................................................................................................ 18 vi Secondary Succession of Soil Seedbank ............................................................................... 21 MATERIALS AND METHODS .................................................................................................. 23 AMCP Efficacy Study .............................................................................................................. 23 Seedbank Succession Study ...................................................................................................... 25 Data Analysis ............................................................................................................................ 27 RESULTS AND DISCUSSION ................................................................................................... 28 AMCP Efficacy Study .............................................................................................................. 28 Seedbank Succession Study ...................................................................................................... 46 Leafy Spurge Stem Density .................................................................................................. 46 Total Seedling Emergence .................................................................................................... 48 Loamy Overflow Seedbank .................................................................................................. 52 Loamy Seedbank ................................................................................................................... 63 Summary ............................................................................................................................... 73 LITERATURE CITED ................................................................................................................. 77 vii LIST OF TABLES Table Page 1. Foliar cover of individual plant species and species richness, evenness, and diversity within the plant community in Fargo, ND prior to [0 mo after treatment (MAT)], and 10 and 14 MAT with aminocyclopyrachlor at 140 g ha-1 ......................................................