The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is one of the main pests in vineyards. At present biological control of the pest is based on the release of hymenopterous parasitoids and coccinellid predators. The effectiveness of an entomopathogenic fungus, Isaria farinosa, as an alternative biological control agent on vine mealybug P. ficus was investigated by using different inoculum densities and different relative humidity levels. The fungus caused more than 80% mortality at 95% relative humidity and at 1 × 108 conidia ml−1 inoculum density. The mortality effects of the fungus decreased in lower humidity levels and lower spore densities. The inhibitory effects of common fungicides, used in vineyards, on I. farinosa were also investigated. Sulphur, copper oxychloride, fosetyl-Al and chlorothalonil did not decrease the effectiveness of I. farinosa as a pathogen of vine mealybug. With the application of tebuconazole, penconazole and mancozeb, the most inhibitory fungicides on the entomopathogen, the mortality rates of mealybugs, inoculated with I . farinosa, decreased from 86% to 42%, 34% and 45%, respectively, in the adult females; from 94% to 51%, 45% and 45%, respectively, in the first nymphal stages; and from 86% to 56%, 49% and 63%, respectively, in ovisacs.