Analysis of three Landsat Enhanced Thematic Mapper Plus (ETM+) images of the Putumayo region of Colombia, one of the primary regions of coca production in Colombia, demonstrated that aerial spraying of defoliants under the US 'Plan Colombia' programme impacted broad swaths of the landscape and had the unintended consequence of defoliating contiguous and interspersed native plant and food crop parcels. Using fractional coverage, field data collections and a hybrid classification, 106 178 ha of impacted land were found, compared with the United Nations Drug Control Program reported reduction in coca of 71 891 ha, an unexplained difference of 34 287 ha. The complex spatial organization of the Colombian coca-producing landscape appeared to confound the spraying of defoliants, and as demonstrated here, many non-coca land cover classes have been affected adversely.