Spectroscopy has emerged in recent years as an effective tool for non-destructive characterization of plant foliar traits related to morphology, physiology and chemistry. These traits control the reflectance, absorptance and transmission of light at molecular, cellular, leaf and canopy levels. As such, measurement of leaf and canopy reflectance can be exploited to enable both the (early) detection of the impacts of pests and pathogens on plants and characterization of possible causes of differences in spectral characteristics among plants. Finally, emerging technologies in imaging spectroscopy -- also called hyperspectral remote sensing -- is enabling new capacities for using imagery to detect and map disease in plants. With upcoming spaceborne missions, we may soon have an unprecedented capacity for pest and pathogen detection at broad spatial scales. This is an exciting time -- but challenges remain. The data volume for such efforts can be a challenge to handle computationally, and we are only beginning to understand the range of interacting factors (genetics, environment) that also affect spectral properties of leaves and canopies. More generally, we have barely scratched the surface in identifying the effects of many diseases that affect many species, not to mention how they affect plants at different stages of plant phenology and disease progression. Here, I present results from synthesis of data across a range of studies to demonstrate both the promise and challenges of spectroscopy on live vegetation for characterizing plant biology.