Leafy spurge (Euphorbia esula L.) is a noxious invasive weed that infests over 1.2 million hectares of land in North America. One of the fundamental needs in leafy spurge management is cost-effective, large-scale, and long-term monitoring of plant populations. Leafy spurge has distinctive yellow-green flower bracts which are spectrally unique when compared to co-occurring green vegetation; the spectral signature is caused by a reduction of chlorophyll allowing various carotenoids to influence the reflectance spectrum. In 1999, Airborne VisibleInfrared Imaging Spectrometer (AVIRIS) data were acquired over Devils Tower National Monument in Northeastern Wyoming. Accuracy of Spectral Angle Mapper classification for flowering leafy spurge was highest using a threshold of 3.5°, which is consistent with both reflectance spectroscopy data and simulations using a canopy radiative transfer model. The minimum detectable cover of flower bracts is about 10%, which is about 35% total cover of leafy spurge, and is ideal for biological control with flea beetles (Aphthona spp.).