Weed Management in Bollgard II® XtendFlexTM Cotton by Justin L. Spradley, B.S. A Thesis In Crop Science Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Dr. J. Wayne Keeling Co-Chair of Committee Dr. Peter A. Dotray Co-chair of Committee Dr. Jason E. Woodward Dr. Guy H. Loneragan Dr. Mark Sheridan Dean of the Graduate School May, 2014 Copyright 2014, Justin L. Spradley Texas Tech University, Justin L. Spradley, May 2014 ACKNOWLEDGMENTS I first thank Jesus for His divine love, creation, and being my savior. I would like to thank my wife Cryctal for all the sacrifices she has made in order for me to accomplish my work, and my daughter Saige for her sacrifice of time with her daddy. I would like to thank Drs. Wayne Keeling and Peter Dotray for allowing me the opportunity to work with their programs. I also thank them for the many hours spent on my trials and thesis work. I have learned a tremendous amount from these gentlemen and appreciate greatly who they are. I would also like to thank Dr. Jason Woodward for all the time he has spent with me in and out of class and at work as well. I gained knowledge of plant pathology from this man, the number one plant pathologist. I thank Dr. Guy Loneragan for being part of my committee and a friend at Texas Tech. I thank you for your time reviewing my work as well as being the professional animal scientist you are. I thank my co-workers and fellow graduate students for the hard work they offered in the field and assisting me on thesis challenges. Co-workers Jacob Reed, Justin Cave, Joel Webb, Shay Morris, Misha Manuchehri, and Rand Merchant helped greatly with field operations, spraying, statistics, data collection, and harvest and deserve many thanks for their time and effort. I thank everyone mentioned for being the best leaders, mentors, and friends a man can have. ii Texas Tech University, Justin L. Spradley, May 2014 I thank Texas Tech University and Texas A&M AgriLife Research for the opportunity and resources to earn a degree and conduct this research. The faculty and staff of both institutions have been wonderful and I appreciate the support they have provided. Special recognition goes to Monsanto for providing partial funding for this research. I am very thankful for their guidance and support. The people at Monsanto have been a pleasure to work with. I also thank my mom Sharron and dad Danny Spradley for all they have done for me. Without their knowledge and wisdom I would not be the man I am today. My brother Dillon for always being there when one is in need. My sister Laurie for being the rock she is. I thank all my extended family for all their love and support. iii Texas Tech University, Justin L. Spradley, May 2014 TABLE OF CONTENTS ACKNOWLEDGMENTS .................................................................................................... ii ABSTRACT ..................................................................................................................... vi LIST OF TABLES .......................................................................................................... viii I. INTRODUCTION .......................................................................................................... 1 II.LITERATURE REVIEW ............................................................................................... 4 History of Weed Management in Cotton ................................................................... 4 Palmer amaranth....................................................................................................... 14 Ivyleaf Morningglory ............................................................................................... 15 Glyphosate-tolerant Cotton ...................................................................................... 17 Glufosinate-tolerant Cotton ...................................................................................... 20 Dicamba-tolerant Cotton .......................................................................................... 22 III.MATERIALS AND METHODS .................................................................................. 25 Field Studies ............................................................................................................. 25 Palmer amaranth, devil’s-claw, and silverleaf nightshade control 2010 ............ 26 Palmer amaranth control 2011 ............................................................................ 27 Palmer amaranth and red morningglory control 2012 ........................................ 27 iv Texas Tech University, Justin L. Spradley, May 2014 2012 Bollgard II® XtendFlexTM Cotton POST – Palmer amaranth and devil’s-claw control ........................................................................................ 28 Ivyleaf morningglory control 2012 ....................................................................... 28 IV.RESULTS AND DISCUSSION .................................................................................... 38 Field Studies ............................................................................................................. 38 Palmer amaranth Glover 2010 ............................................................................ 38 Devil’s-claw Glover 2010 .................................................................................... 41 Silverleaf nightshade Glover 2010 ....................................................................... 42 Palmer amaranth 2011 ........................................................................................ 43 Palmer amaranth Lorenzo, TX 2012 .................................................................... 47 Red morningglory Lorenzo, TX 2012 ................................................................... 49 Palmer amaranth Glover Farm 2012 .................................................................. 50 Devil’s-claw Glover Farm 2012 .......................................................................... 51 Palmer amaranth control Lubbock Station (301) Farm 2012 ............................. 52 Ivyleaf morningglory I control Lubbock Station (301) Farm 2012 ..................... 53 Ivyleaf morningglory II control Lubbock Station (301) Farm 2012 .................... 54 V. SUMMARY AND CONCLUSIONS ............................................................................... 68 LITERATURE CITED ..................................................................................................... 73 v Texas Tech University, Justin L. Spradley, May 2014 ABSTRACT Bollgard II® XtendFlexTM cotton could improve management of many problem annual and perennial weeds on the Texas High Plains. Weed species including Palmer amaranth (Amaranthus palmeri S. Wats.), devil’s-claw (Proboscidea louisanica Thell.), silverleaf nightshade (Solanum elaeagnifolium Cav.), ivyleaf morningglory (Ipomoea hederacea Jacq.), and red morningglory (Ipomoea coccinea L.) are not always effectively controlled with glyphosate [N-(phosphonomethyl)glycine] alone, but residual herbicides such as trifluralin [2,6-dinitro-N,N-dipropyl-4- (trifluoromethyl(benzenamine)] combined with dicamba [3,6-dichloro-2- methoxybenzoic acid], glufosinate-ammonium [2-amino-4- (hydroxymethylphosphinyl)butanoic acid monoammonium salt] or glyphosate may improve control. Bollgard II® XtendFlexTM technology may acknowledge the utility of alternative modes of action in managing identified glyphosate-resistant Palmer amaranth and other weed populations. The objectives of the studies were to 1) evaluate dicamba applied preemergence (PRE) and postemergence (POST) alone or in combination with glufosinate or glyphosate for Palmer amaranth, devil’s-claw, and ivyleaf morningglory control in Bollgard II® XtendFlexTM cotton, 2) compare Palmer amaranth control with dicamba-based treatments in Bollgard II® XtendFlexTM cotton to standard weed management programs in cotton, and 3) determine cotton response to glyphosate, glufosinate, and dicamba and lint yield in Bollgard II® XtendFlexTM cotton. vi Texas Tech University, Justin L. Spradley, May 2014 Field trials were conducted in 2010, 2011 and 2012 at the Texas A&M AgriLife Research and Extension Center in Lubbock, TX and near Lorenzo, TX in 2012 to assess the control of the aforementioned weed species in Bollgard II® XtendFlexTM cotton. Evaluations were made in plots with or without trifluralin preplant incorporated (PPI) followed by (fb) dicamba, glufosinate, or glyphosate applied either alone or tank-mixed in different combinations. Preemergence treatments included glyphosate and dicamba alone and in combination. The treatments that followed a PRE application were applied at timings that included early-postemergence (EPOST), delayed early-postemergence (D-EPOST), postemergence, mid-postemergence (MPOST), and layby. Results indicated that >90% Palmer amaranth control was achieved when dicamba was applied PRE and EPOST and fb glufosinate MPOST 14 days after treatment (DAT). Glyphosate applied PRE, POST, and MPOST resulted in the greatest control of devil’s-claw 14 DAT; whereas silverleaf nightshade control was similar for all 14 DAT MPOST treatments and ranged from 65 to 83%. Trifluralin PPI fb glyphosate + dicamba or glyphosate + dicamba + acetochlor EPOST fb glyphosate or glyphosate + dicamba MPOST controlled ivyleaf morningglory greater than all other treatments. Furthermore, results from these studies indicate that a system-based approach