This study addresses the necessity to provide fast assessment of pesticide coverage on plants, which is required for saving the expensive compounds and for protecting the environment against overdosing. The feasibility of applying several optical methods for direct detection of the pesticides on plants has been investigated. In order to overcome the matrix effect, which is related to plant fluorescence emission and to physiological spectral interferences, we suggest the application of a fluorescent labeling agent, in form of nano- and micro-crystallites. The coverage assessment is based on the spectral effects related to the interaction of these crystallites with the pesticides. Among the studied features are the fluorescence quenching/enhancement, spectral shifts and fluorescence lifetimes. It has been found that these spectral features are adequate for mapping the pesticides on plant surfaces, and assessing their coverage. Direct charge-coupled-device (CCD) fluorescence imaging was found as a low-cost adequate method, while Fourier transform spectral imaging provided more specific and accurate results.