Available at: https://digitalcommons.calpoly.edu/theses/3384
Date of Award
6-2026
Degree Name
MS in Agriculture - Plant Protection Science
Department/Program
Horticulture and Crop Science
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Shunping Ding
Advisor Department
Horticulture and Crop Science
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
Fusarium wilt, caused by Fusarium oxysporum f. sp. lactucae (FOLac), is a damaging soilborne disease of lettuce (Lactuca sativa L.) for which few effective management options currently exist. This thesis evaluated whether commercially available biological and low-risk fungicide products can suppress Fusarium wilt and deliver measurable biostimulant effects in lettuce, integrating evaluations across greenhouse, small-plot field, and commercial field environments. In the greenhouse, three Fusarium wilt suppression experiments and a separate heat-stress physiology trial were conducted, followed by replicated small-plot field trials under artificial inoculation. Across these experiments, no biological product or low-risk fungicide consistently reduced disease severity area under the disease progress curve relative to inoculated controls, and no treatment significantly affected lettuce physiological responses or biomass under heat stress. In commercial iceberg lettuce fields near Santa Maria, California, three products selected in part for cost-effectiveness were applied through drip chemigation, with disease and canopy development monitored at the plot scale using ground assessments and unmanned aerial vehicle (UAV) multispectral imagery. None of the products provided meaningful disease suppression under commercial conditions; however, UAV-derived vegetation indices (NDVI, NDRE, LAI, and ALN) were strongly correlated with ground-measured disease severity, reliably capturing spatial patterns of Fusarium wilt within fields. Collectively, these results indicate that the biological and low-risk products evaluated did not provide reliable suppression of Fusarium wilt or detectable biostimulant benefits under the conditions tested, while demonstrating that remote sensing can support spatial disease monitoring. These findings emphasize the need for integrated management strategies and for rigorous, field-scale validation of commercial biological products before adoption.