Field and Greenhouse Bioassays to Determine Rotational Crop Response to Mesotrione Residues by Rachel Nicole Riddle A Thesis presented to The University of Guelph In partial fulfilment of requirements for the degree of Master of Science in Crop Science Guelph, Ontario, Canada © Rachel N. Riddle, January, 2012 ABSTRACT FIELD AND GREENHOUSE BIOASSAYS TO DETERMINE ROTATIONAL CROP RESPONSE TO MESOTRIONE RESIDUES Rachel N. Riddle Advisors: University of Guelph, 2012 Dr. J. O’Sullivan Dr. C.J. Swanton Field and greenhouse bioassay experiments were conducted to evaluate the effects of mesotrione soil residues on injury and yield of soybean, green bean, pea, cucumber, sugar beet and lettuce. There was a significant difference of mesotrione carryover between studies which can be explained by differences in soil pH and moisture. The conventional and the simulated field residue carryover studies successfully measured mesotrione persistence and rotational crop sensitivity. The simulated residue carryover study provided a more rigorous test of rotational crop sensitivity to mesotrione residues than the conventional residue carryover study, especially at higher doses for the more sensitive crops. The greenhouse bioassay was a simple and sensitive tool in detecting small amounts of herbicides present in the soil. Dose-response curves developed for sugar beet and green bean indicate similarities between results from the greenhouse and from the field mesotrione residue carryover study. Under similar environmental and soil conditions to those observed in these studies and using similar dose applications, sugar beet, green bean and cucumber injury and yield reductions are likely when these crops are grown in soils containing mesotrione residues. ACKNOWLEDGEMENTS I would like to thank my advisors, Dr. John O’Sullivan and Dr. Clarence Swanton for taking me on as a graduate student and providing me with a wonderful learning opportunity. Dr. John O’Sullivan, thank you for your constant support and encouragement throughout this process. I could always count on your sense of humour to ease the stress of a frustrating moment. Dr. Clarence Swanton, thank you for your advice and efforts to include me as a member of the Weeds Lab on campus. I would also like to thank Dr. Chris Hall, Dr. Darren Robinson and Harold Wright for your assistance with everything from data collection, to statistics, and to support with residue analysis and soil spiking. This research would not have been possible without Robert Grohs. I cannot express how much I appreciated your technical guidance and assistance with everything from the field trials to the greenhouse to the write-up, and for your patience and understanding throughout this entire process. Many thanks to the farm crew, Ernie Andrews, Larry Frost, Paul Splinter and Bill Genery and manager, Wally Andres, at the Simcoe Research Station, for providing support in the field and in the greenhouse. I am also so grateful for all the hard work and great care that summer students took while working with me on my research. Thank you to Syngenta Crop Protection Canada for providing funding for this research as well as providing materials and method guidance for the greenhouse bioassays. Lastly I would like to thank my family and friends who have made sacrifices in order to see that this research be finished and defended. A special thank you to my husband Greg, my daughter Ella and my parents, Bonnie and Howard, whose encouragement, and understanding has made this long process just a little easier. iii TABLE OF CONTENTS ABSTRACT ....................................................................................................................... ii ACKNOWLEDGEMENTS ................................................................................................. iii TABLE OF CONTENTS ................................................................................................... iv LIST OF TABLES ............................................................................................................. vi LIST OF FIGURES ...........................................................................................................vii 1.0 INTRODUCTION ......................................................................................................... 1 2.0 LITERATURE REVIEW ............................................................................................... 4 2.1 Mesotrione ............................................................................................................... 4 2.1.1 Classification ..................................................................................................... 4 2.1.2 Mode of action .................................................................................................. 5 2.1.3 Use patterns ...................................................................................................... 6 2.2 Factors influencing residue persistence .................................................................. 7 2.2.1 Soil characteristics ............................................................................................ 9 2.2.2 Environmental conditions ................................................................................ 11 2.2.1 Herbicide use patterns .................................................................................... 11 2.2.2 Herbicide properties ........................................................................................ 12 2.3 Mesotrione in the soil ............................................................................................. 12 2.4 Phytotoxicity and rotational crops .......................................................................... 15 2.5 Methods of detecting herbicide residues ............................................................... 17 2.6 Dose-response curves ........................................................................................... 19 2.7 Simulated carryover of herbicides ......................................................................... 20 2.8 Research hypothesis ............................................................................................. 22 3.0 CROP RESPONSE TO CARRYOVER OF MESOTRIONE RESIDUES IN THE FIELD (CONVENTIONAL AND SIMULATED RESIDUE CARRYOVER) ....................... 25 3.1 Abstract.................................................................................................................. 25 3.2 Introduction ............................................................................................................ 26 3.3 Materials and methods .......................................................................................... 28 3.3.1 Conventional residue carryover study ............................................................. 28 3.3.2 Simulated residue carryover study .................................................................. 31 3.3.3 Statistical analysis ........................................................................................... 31 3.4 Results and discussion .......................................................................................... 32 3.4.1 Sugar beet ...................................................................................................... 32 3.4.2 Cucumber ....................................................................................................... 34 3.4.3 Green bean ..................................................................................................... 35 iv 3.4.4 Pea .................................................................................................................. 36 3.4.5 Soybean .......................................................................................................... 37 3.4.6 Chemical analysis of mesotrione carryover .................................................... 38 3.5 Conclusions ........................................................................................................... 39 4.0 GREENHOUSE BIOASSAY TO DETERMINE CROP RESPONSE TO MESOTRIONE RESIDUES ............................................................................................. 53 4.1 Abstract.................................................................................................................. 53 4.2 Introduction ............................................................................................................ 54 4.3 Materials and methods .......................................................................................... 55 4.4 Results and discussion .......................................................................................... 60 4.4.1 Greenhouse bioassay (using field samples of mesotrione treated soil) .......... 60 4.4.2 Greenhouse bioassay (soil spiked with mesotrione of known concentrations)62 4.4.3 Greenhouse bioassay related to field residue carryover study ....................... 63 4.5 Conclusions ........................................................................................................... 64 5.0 GENERAL DISCUSSION AND CONCLUSIONS ...................................................... 74 5.1 Research contributions .......................................................................................... 74 5.2 Research limitations .............................................................................................. 78 5.3 Future research ....................................................................................................