Fluopicolide does not show any cross resistance to other commercial oomycete fungicides. lt controls fungi resistant to phenylamides, strobilurins and dimethomorph, suggesting that fluopicolide has a novel mode of action. Zoospores swell and lyse rapidly upon treatment with fluopicolide. Irnmunolocalization studies showed that a cytoskeleton-associated protein, spectrin-like protein, was delocalized after fluopicolide treatment. This happens in both zoospores and hyphae of P. infestans. Spectrins play a role in membrane stability in mammalian cells, but are poorly characterized in fungi. Here they might have an important role in maintaining membrane integrity as well. Western blot experiments indicated the presence of spectrin-like protein in a crude extract of P. infestans and purification of the relevant proteins is ongoing. The possibility that the observed cellular delocalization of spectrin-like protein is the result of an effect on another, related target cannot be excluded yet. The role of spectrin-like proteins in oomycete development and the target of fluopicolide need further investigation.