EVALUATION OF SEED AND DRENCH TREATMENTS FOR MANAGEMENT OF DAMPING-OFF AND SEEDLING BLIGHT PATHOGENS OF SPINACH FOR ORGANIC PRODUCTION By JAIME ANNE CUMMINGS A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN PLANT PATHOLOGY WASHINGTON STATE UNIVERSITY Department of Plant Pathology DECEMBER 2007 To the Faculty of Washington State University: The members of the Committee appointed to examine the thesis of JAIME ANNE CUMMINGS find it satisfactory and recommend that it be accepted. ____________________________________ Chair ____________________________________ ____________________________________ ____________________________________ ii ACKNOWLEDGEMENTS Professional I would like to thank my advisor, Dr. Lindsey du Toit, for welcoming me into the Vegetable Seed Pathology Program at WSU Mount Vernon Northwestern Washington Research and Extension Center, and for her patience and enthusiasm in introducing me to the field of Plant Pathology. I am grateful for her advice and guidance. The experiences and skills gained while working with her are immeasurable. I also thank my committee members; Dr. Debra Inglis, Dr. Carol Miles, and Dr. Frank Dugan, for their collective and individual contributions which made this project a success. I would like to extend a special thank you to Dr. Inglis for her time, attention, and guidance; her contributions to the successful completion of this degree are greatly appreciated. I would like to thank the WSU Center for Sustaining Agriculture and Natural Resources Organic Research Program for funding this project and Dr. Miles for her part in securing the funding. Additionally, I would like to thank Dr. Dugan for his time and guidance while I was in Pullman and new to the department. I would like to extend my gratitude to the entire WSU Mount Vernon NWREC faculty and staff for all their assistance and encouragement, and especially to the entire VSP team. Particularly Mike Derie for his expertise, patience, and assistance with many aspects of my project; Louise Brissey for all her expertise and the hours she contributed at the microscope and elsewhere, as well as for her undying encouragement; Barbara Holmes for all of her technical assistance with the greenhouse and field trials, and incredible willingness to do whatever needed to be done; and Kerri Brooks for her efficiency and accuracy with the germination assays and many other contributions, including her spectacular personality which made work fun. I would also like to acknowledge Carl Libbey for all his support and contributions as my ‘go-to-man’ at the station for so many uncountable things. Thank you to Ron Dralle, Dan Gorton, and Juan iii Alonso for all they did to ensure that the facilities and fields were suitable for research, and to the office staff, Pat King, Kathy Gleissner, and Jeanne Burritt for answering all my questions and for processing all my paperwork. Additionally, I would like to thank the ladies in the office in Pullman, Cheryl Hagelganz and Mary Stormo, for all of their assistance. Personal I would like to thank Aaron Jacobsen for his support and encouragement, as well as his selfless tolerance and understanding throughout my time as a student. I would also like to thank my parents, Jim and Judy Cummings for their support and encouragement. I thank Moosie for being a constant and fantastic source of comfort and relaxation. Additionally, I would like to acknowledge and thank Leigh Ann Harrison for all her advice, guidance and support, and for being a terrific friend who always had an open ear. iv EVALUATION OF SEED AND DRENCH TREATMENTS FOR MANAGEMENT OF DAMPING-OFF AND SEEDLING BLIGHT PATHOGENS OF SPINACH FOR ORGANIC PRODUCTION Abstract by Jaime Anne Cummings, M.S. Washington State University December 2007 Chair: Lindsey du Toit There are many concerns regarding losses to seedborne and soilborne pathogens in organic production systems because of limited effective options available for disease management that satisfy organic standards. Seed treatments can be inexpensive and effective, including those with biological control agents (BCAs). However, the reliability of BCAs for disease control is affected by crop species, whether a pathogen is seedborne or soilborne, and numerous abiotic factors. The efficacy of a range of seed and drench treatments for control of soilborne seedling blight and damping-off pathogens was investigated using spinach as a model small-seeded vegetable. The seed and drench treatments included those that were EPA registered and approved for use in organic agriculture as defined by the National Organic Standards, and those that were being developed for registration and compliance with organic standards. Greenhouse inoculation rate trials were completed for each of three soilborne pathogens, Fusarium oxysporum f. sp. spinaciae, Pythium ultimum, and Rhizoctonia solani. Results were then used to evaluate 14 seed and drench treatments in greenhouse trials against each pathogen. For P. ultimum, two experimental seed treatments, Experimental #1 and #2, provided equivalent control to that provided by a conventional fungicide seed treatment, Apron XL LS; while Natural II, Natural X, and Subtilex seed treatments each suppressed damping-off significantly in only one of v two trials. For F. oxysporum f. sp. spinaciae, drenches with a compost tea or Prestop, and seed treatment with Yield Shield suppressed post-emergence wilt significantly in one of two trials; but no treatment was highly effective. For R. solani, Experimental #1 and Natural II seed treatments reduced damping-off as effectively as a drench with the conventional fungicide Terraclor. Seed health assays revealed that treatments with Experimental #1, Experimental #2, or Mycostop Mix significantly reduced the incidence of seedborne Verticillium and Alternaria. Natural II and Natural X seed treatments significantly reduced early germination in seed germination assays. Selected treatments were evaluated further under field conditions at three locations in western Washington. There was little consistency in results among field trials. However, Experimental #1 and #2 seed treatments consistently caused significantly earlier emergence than the other treatments. In contrast, the compost tea drench resulted in low total emergence and low spinach biomass, but also low post-emergence wilt in two of three trials. vi TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................................. iii ABSTRACT.....................................................................................................................................v LIST OF TABLES......................................................................................................................... ix LIST OF FIGURES .........................................................................................................................x CHAPTER 1. Literature Review 1.1. Soilborne fungal plant pathogens..................................................................................1 1.2. Biological control of soilborne plant pathogens ...........................................................4 1.3. Seed pathology and seed treatments .............................................................................6 1.4. Organic production .....................................................................................................10 1.5. Spinach 1.5.1. Spinach and spinach seed production ..........................................................13 1.5.2. Diseases affecting spinach and spinach seed production.............................15 1.6. Fusarium wilts 1.6.1. Background and importance ........................................................................17 1.6.2. Fusarium oxysporum ...................................................................................17 1.6.3. Management of Fusarium wilts ...................................................................18 1.7. Pythium species as plant pathogens 1.7.1. Background and importance ........................................................................22 1.7.2. Pythium ultimum ..........................................................................................23 1.7.3. Management of Pythium damping-off.........................................................23 1.8. Rhizoctonia species as plant pathogens 1.8.1. Background and importance ........................................................................25 1.8.2. Rhizoctonia solani........................................................................................26 1.8.3. Management of Rhizoctonia damping-off and seedling blight....................27 1.9. Conclusion and research needs ...................................................................................29 1.10. Literature cited..........................................................................................................31 2. Greenhouse pathogen inoculation rate trials, and seed and drench treatment trials for organic production 2.1. INTRODUCTION......................................................................................................42 2.2. MATERIALS AND METHODS 2.2.1. Pathogen isolates..........................................................................................45 2.2.2. Preparation of inocula..................................................................................48 2.2.3. Inoculation of potting mix for greenhouse inoculation