Technical Abstract: The incidence and severity of many plant diseases depend on organisms besides pathogens, hosts, and humans. Plant diseases may be facilitated by various kinds of organisms that serve as alternate hosts, vectors, or pre-disposing agents, while other organisms limit disease as pathogen antagonists. Several species of insects and other arthropods facilitate plant disease as vectors, pre-disposing agents, or both. Among the most notorious insects that facilitate plant disease are aphids, whiteflies, scale insects, planthoppers and treehoppers—phloem-feeding insects that are classified in the Homoptera and generally infest leaves and stems. The purpose of this article is to review how homopterans facilitate plant diseases, with a focus on briefly comparing and contrasting the relationship between homopterans and two diseases, namely Barley yellow dwarf and sooty mold. Characteristics of the two diseases and methods for their management are discussed.