EVALUATING THE EFFECTS OF SOLID VERMICOMPOST APPLICATIONS ON PLANT GROWTH AND PEST DENSITIES OF NAVEL ORANGE TREES A Thesis Presented to the Faculty of California State Polytechnic University, Pomona In Partial Fulfillment Of the Requirements for the Degree Master of Science In Plant Science By Deborah L. Nardo 2020 SIGNATURE PAGE THESIS: EVALUATING THE EFFECTS OF SOLID VERMICOMPOST APPLICATIONS ON PLANT GROWTH AND PEST DENSITIES OF NAVEL ORANGE TREES AUTHOR: Deborah L. Nardo DATE SUBMITTED: Fall 2020 Department of Plant Science Dr. Anna L. Soper _________________________________ Thesis Committee Chair Plant Sciences Dr. Jon C. Phillips _________________________________ Department Chair Agribusiness & Food Industry Management /Agricultural Science Dr. Srdjan Lemez _________________________________ Assistant Professor Kinesiology Ben Lehan, M.S. _________________________________ Lecturer Plant Sciences ii ACKNOWLEDGEMENTS This thesis is possible due to the guidance and support of my colleagues, professors, and mentors at Cal Poly Pomona. Dr. Anna Soper has been an invaluable mentor and advisor since I began my undergraduate research at Cal Poly Pomona. I greatly appreciate her unwavering support. Dr. Jon Phillips afforded me the opportunity to teach in his department under his guidance and to assist him in ancillary projects. His support has been tremendous. Dr. Srdjan Lemez has propelled me to continually push myself in academic endeavors. I would not have set out to master SPSS and JASP if it hadn't been for his perspective on statistics. In addition, he inspires me to continually improve my writing skills. Professor Ben Lehan has been an enormous influence on my research. I am grateful for the support he has given me since my project began. Dr. Valerie Mellano, Chair of the Plant Sciences Department, continues to be an inspiration to me. Renee Murphy, colleague and fellow M.S. candidate, has assisted me in numerous aspects of my research project. I cannot begin to thank her enough. Muriel Walker-Waugh, Chemistry Professor at Santa Monica College, has been my ultimate mentor since my Freshman year. I aspire to her level of greatness on a daily basis. This project was funded by a grant from the Agricultural Research Institute, Grant Number 15-04-219. iii ABSTRACT The citrus industry has been devastated by pests and diseases in the past two decades that creates challenges in successful production. Unique control methods are needed to combat these threats in order to save commercial trees from catastrophic losses and reduce dependency upon pesticides. Vermicompost, a soil medium created from decomposition of organic matter by worms, has been demonstrated to improve plant yield, growth, and quality in a wide range of species. Furthermore, it has shown promise in decreasing pest densities and increasing resistance to pest and disease attacks. To evaluate the effects of solid vermicompost on citrus tree growth and pest densities, 40 field-planted two-year-old citrus trees were subjected to the following treatments: a layer of vermicompost below and surrounding the roots, a layer of vermicompost above the soil around the root zone, a layer both above and below the soil, and a control group with no treatment given. Trunk diameter, fruit yield, weight, and quality, and Asian Citrus Psyllid, Citrus leafminer, and citrus thrip density levels were measured. Data were analyzed with SPSS statistical software (Version 26) in a two-fold procedure of descriptive i.e. frequencies and variance) and inferential (i.e. ANOVA, MANOVA, and Repeated Measures ANOVA) statistics with post-hoc Tukey analysis for growth and quality data, and RMANOVA with post-hoc Fisher's LSD for pest density (P<0.05). Results showed that trees treated with solid vermicompost layered around the root zone at planting had greater trunk diameter growth. Results for pest pressure, fruit production, and fruit quality were statistically insignificant. Further studies should focus on pairing solid vermicompost at the root zone with foliar aqueous vermicompost applications, as well as monitoring these trees in subsequent growing seasons. iv TABLE OF CONTENTS SIGNATURE PAGE ........................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................ iii ABSTRACT ...................................................................................................................... iv LIST OF FIGURES ....................................................................................................... viii LITERATURE REVIEW ................................................................................................. 1 California Citrus Industry ............................................................................................ 1 Citrus Growth Characteristics ..................................................................................... 2 Citrus Pests and Biotic Pressures ................................................................................. 3 Current Methods of Pest Control ................................................................................. 6 Vermicompost ................................................................................................................ 7 Conventional Composting vs Vermicomposting ......................................................... 8 Vermicompost and Pest Damage ................................................................................ 10 Vermicompost and Plant Growth Improvements .................................................... 11 Vermicompost and Citrus ........................................................................................... 12 STUDY PURPOSE AND OBJECTIVES ...................................................................... 13 METHODOLOGY .......................................................................................................... 15 Planting of Trees .......................................................................................................... 15 Soil Profile .................................................................................................................... 16 Vermicomposting Material ......................................................................................... 17 v Irrigation ...................................................................................................................... 17 Plant Growth Assessments .......................................................................................... 17 Fruit Assessments ........................................................................................................ 18 Pests............................................................................................................................... 18 Asian Citrus Psyllid .................................................................................................. 18 Citrus Thrips ............................................................................................................. 19 Citrus Leafminer ....................................................................................................... 19 Statistics and Data Analysis ........................................................................................ 20 RESULTS ......................................................................................................................... 21 Plant Growth Results .................................................................................................. 21 Fruit Production Results ............................................................................................. 21 Pest Density Results ..................................................................................................... 22 Asian Citrus Psyllid .................................................................................................. 22 Thrips ........................................................................................................................ 22 Leafminer .................................................................................................................. 22 DISCUSSION ................................................................................................................... 24 Limitations and Future Directions ............................................................................. 26 CONCLUSION ................................................................................................................ 28 Key Findings ................................................................................................................ 28 Practical Implications and Proposed Impact ............................................................ 28 vi SOURCES ........................................................................................................................32 FIGURES .........................................................................................................................38 APPENDIX.......................................................................................................................42 vii LIST OF FIGURES Figure 1: Trunk Diameter Growth (mm)............................................................................38 Figure 2: Mean Fruit Pieces per Tree..................................................................................38 Figure 3: