Observation of recent epidemics of gummy stem blight, caused by Mycosphaerella melonis, on cucurbits indicated a relationship with high incidence of either cucumber beetle feeding or powdery mildew. In 2 field experiments, gummy stem blight was reduced significantly in plots that were caged to exclude insects. In addition to predisposing plants to infection, the striped cucumber beetle (Acalymma vittatum) served as a vector of the causal fungus. In laboratory experiments, both powdery mildew and melon aphids [Aphis gossypii] markedly predisposed cucurbit leaves to M. melonis. Filtered, aqueous washings of mildewed leaves and aphid-infested leaves provided the same level of disease stimulation as the organisms themselves. Uninjured cucurbit leaves were virtually immune to unamended M. melonis, but they were susceptible when inoculum was amended with 0.1% sucrose and 0.05% hydrolyzed casein. Late-summer foliar necrosis of cucurbits in Kentucky [USA] may be caused by the interaction of powdery mildew, insects and M. melonis.