This work reports a controlled-release pesticide platform based on fenobucarb-loaded core-shell nanofibers fabricated by coaxial electrospinning. Polylactic acid served as the biodegradable outer shell, while fenobucarb was incorporated into the inner core. The produced fibers had diameters ranging from 200 to 800 nm, with an average value of approximately 530 nm, and transmission electron microscopy confirmed the core-shell configuration. The loading content reached 17.976%, indicating effective incorporation of the active compound. Release experiments showed sustained fenobucarb release over a 30-day period, with an initial lag phase followed by a diffusion-driven process that was best described by the Higuchi model. Two formulation types, wettable powder and suspension concentrate, were developed and assessed on tomato crops under field conditions in Vietnam. In the preliminary field assessment, the suspension concentrate and wettable powder formulations showed descriptive efficacy values of 89.9% and 81.0% after 30 days, respectively, without visible phytotoxicity. Because the field assessment did not include replicated randomized plots, these values should be interpreted as preliminary evidence rather than statistically confirmed treatment superiority.