Imazalil [1‐[2‐(2,4‐dichlorophenyl)‐2‐(2‐propenyloxyl‐ethyl]‐1 H imidazole] is a systemic fungicide that is toxic to a number of plant pathogens, particularly species of Penicillum. Its activity is based on the inhibition of mold sporulation on fruit skin, which makes it one of the most commonly used fungicide in post‐harvest citrus treatments for fruit preservation during storage, shipping, and marketing. Due to its wide application, the presence of imazalil needs to be monitored to avoid the excessive and/or improper use. This work reports a complete analysis of the Fourier‐transform infrared spectroscopy and Raman spectra of imazalil as a pure compound as well as in the commercial product for agricultural use; the band assignment relays in the vibrational predictions acquired by quantum‐chemical calculations (B3LYP/6–311 + g(2df, p)) for the imazalil molecule. An analytical application of surface‐enhanced Raman spectroscopy (SERS) is also presented here. It is done so by using a novel, low‐cost, and sensitive SERS‐active substrate built with silver nanoparticles supported on a Si/ZnO nanowires platform to detect traces of imazalil in aqueous solutions. Comparison between the Raman and SERS spectra allowed the characterization of the interaction between the pesticide and the silver nanoparticle surface.