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  • TERMINATION REPORT

    MISSISSIPPI SOYBEAN PROMOTION BOARD

    FY 2007

    Title: Strategies to Monitor and Control Glyphosate-resistant Weeds

    Principal

    Investigators: Daniel H. Poston, Delta Research and Extension Center

    Clifford H. Koger, USDA-ARS Crop Production and Genetics Research Unit

    David R. Shaw, Plant and Soil Sciences Department

    Objectives:

    1. Monitor and screen weed populations suspected of being glyphosate-resistant.

    2. Develop management strategies for glyphosate-resistant and -susceptible

    horseweed.

    3. Determine the optimum time to control horseweed by documenting emergence

    and growth patterns for horseweed at various locations in Mississippi.

    4. Disseminate information to producers in a timely fashion.

    Objective 1: Plant materials and seed of weeds suspected of being resistant to glyphosate

    continue to be collected from various locations around the state. Glyphosate titrations in

    the field and greenhouse as well as assay techniques, reported on in earlier reports, have

    been used successfully to determine resistance in horseweed populations from across the

    state. Glyphosate resistant horseweed has been documented as far south as Greenville,

    MS and is suspected of being more widely disseminated throughout the state. More

    complaints of glyphosate failing to control horseweed were reported this past growing

    season and more alternative chemistries, mostly cloransulam, were used to control this

    weed in soybean. Italian ryegrass populations with 3-fold tolerance to glyphosate have

    been confirmed and alternative control methods are being evaluated. Glyphosate tolerant

    Italian ryegrass could potentially pose a larger threat to crop production than glyphosate-

    resistant horseweed because there are few affordable control alternatives. This raises

    great concern because many herbicides that are added to glyphosate to control resistant

    horseweed reduce the control of ryegrass.

    Pigweed plants and seed were collected from several locations, but no confirmed cases of

    pigweed or waterhemp resistance have been documented to date. Giant ragweed is

    another weed that we suspect of developing increased tolerance to glyphosate in

    Mississippi, however in many cases it may represent the encroachment of this weed into

    fields from field borders and this weed was never effective controlled by glyphosate.

    Reports of poor Johnsongrass control with glyphosate raised perhaps the most concern

    among our research group. We investigate on location where glyphosate failed to control

    Johnsongrass. Coincidentally, this occurred about the time that glyphosate-resistant

    Johnsongrass was confirmed in Argentina. Rhizomes were collected from this location,

    but we have been unable to confirm resistance at this location as of yet. Plans are in

  • place to closely monitor this location in 2007. Glyphosate-resistant Johnsongrass poses

    perhaps the largest threat to date for production systems in Mississippi.

    SEE ALSO ATTACHED MANUSCRIPT REPRINT.

    Objectives 2

    SEE ATTACHED DOCUMENTS.

    Objective 3:

    SEE ATTACHED DOCUMENTS.

    Objective 4: To date, two journal articles associated with this project have been

    accepted. In addition, one M.S. thesis has been completed and at least two articles will be

    submitted within the next month. Findings from this project have been presented at

    numerous meetings around the state, region, and nation including the DREC field day,

    grower meetings, The Southern Weed Science Society annual meeting, The Weed

    Science Society of America annual Meeting, The Beltwide Cotton Conference, The

    Mississippi Joint Pest Management Conference, The Delta Ag Expo, and the Mississippi

    Crop College. Findings have also been featured in the Delta Business Journal and other

    popular press articles.

  • Appendix A

    FIELD EMERGENCE OF HORSEWEED [Conyza canadensis (L.) Cronq.] AND

    CONTROL UTILIZING TILLAGE AND HERBICIDES

    By

    Thomas William Eubank III

    A Thesis

    Submitted to the Faculty of

    Mississippi State University

    in Partial Fulfillment of the Requirements

    for the Degree of Master of Science

    in Weed Science

    in the Department of Plant and Soil Sciences

    Mississippi State, Mississippi

    December 2006

    FIELD EMERGENCE OF HORSEWEED [Conyza canadensis (L.) Cronq.] AND

    CONTROL UTILIZING TILLAGE AND HERBICIDES

    By

  • Thomas William Eubank III

    Approved:

    Daniel H. Poston David R. Shaw

    Associate/Extension Professor of Giles Distinguished Professor of

    Weed Science Weed Science

    (Co-Major Professor) (Co-Major Professor)

    D. Wayne Wells Daniel B. Reynolds.

    Extension Professor Professor of Weed Science

    (Minor Professor) (Committee Member)

    Clifford H. Koger William Kingery

    USDA Research Agronomist Graduate Coordinator of

    (Committee Member) the Department of Plant & Soil

    Sciences

    Vance H. Watson

    Dean of the College of Agriculture

    and Life Sciences

  • Name: Thomas William Eubank III

    Date of Degree: December 8, 2006

    Institution: Mississippi State University

    Major Field: Weed Science

    Major Professor: Dr. Daniel H. Poston

    Title of Study: FIELD EMERGENCE OF HORSEWEED [Conyza canadensis (L.)

    Cronq.] AND CONTROL UTILIZING TILLAGE AND HERBICIDES

    Pages in Study: 49

    Candidate for Degree of Master of Science

    Horseweed has been documented in many crops around the world and is

    listed as being a problem weed in no-till production systems. Horseweed has developed

    resistance to many herbicides including glyphosate. Field experiments were conducted

    from 2004 to 2006 in the Mississippi Delta to evaluate the field emergence of horseweed

    and various treatment programs for its control.

    Field emergence of horseweed was observed occurring primarily in the fall of the

    year, September through November, when temperatures were between 16 to 23 C with

    later emergence occurring in January through April when temperatures were from 5 to 16

    C. Tillage in September followed by herbicide in March gave 100% control of horseweed

    across all locations. Glyphosate + 2,4-D and glyphosate + dicamba provided 90% or

    better horseweed control 4 WAT both years. Glufosinate-based burndowns provided 81

    to 97% horseweed control, and soybean yields were generally similar with all

    glufosinate-based treatments.

  • ii

    DEDICATION

    I would like to dedicate this work to my wife (Beth Eubank) and children (Adelle

    and Will Eubank). Your love, patience and support have allowed me to pursue my

    dreams, and I thank you.

  • iii

    ACKNOWLEDGEMENTS

    I would like to express my sincere appreciation to Dr. Daniel Poston for allowing

    me to further my education. Your patience and mentoring have enabled me to broaden

    my horizons and brighten my future. I would also like to thank Drs. David Shaw, Dan

    Reynolds, Trey Koger and Wayne Wells for their time in serving as members of my

    graduate committee.

    A special thanks to Russel Coleman, Brewer Blessitt, Hunter Doty, Troy Gibson,

    Beth Graves, and Robert Wells who have all contributed to my research efforts in the

    field, lab and office. I appreciate all your hard work.

  • iv

    TABLE OF CONTENTS

    Page

    DEDICATION ......................................................................................................... ii

    ACKNOWLEDGEMENTS...................................................................................... iii

    LIST OF TABLES ................................................................................................... v

    LIST OF FIGURES.................................................................................................. vi

    CHAPTER

    I. INTRODUCTION......................................................................................... 1

    LITERATURE CITED ................................................................................. 9

    II. FIELD EMERGENCE OF HORSEWEED AND IMPACT OF

    HERBICIDE AND TILLAGE TIMING ON CONTROL.............................. 13

    Abstract ........................................................................................................ 13

    Introduction .................................................................................................. 14

    Materials and Methods .................................................................................. 17

    Horseweed Emergence ............................................................................ 18

    Tillage and Herbicide Controls................................................................ 18

    Results and Discussion.................................................................................. 19

    Horseweed Emergence ............................................................................ 19

    Tillage and Herbicide Controls................................................................ 21

    LITERATURE CITED ................................................................................. 24

    III. GLYPHOSATE-RESISTANT HORSEWEED CONTROL USING

    GLYPHOSATE-, PARAQUAT-, AND GLUFOSINATE-BASED

    HERBICIDE PROGRAMS.........

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