Antigens were isolated from the walls of Oidium conidia by a simple ex
traction method. Polyclonal antiserum was produced against these antig
ens and an immunofluorescent assay was developed to detect overwinteri
ng mycelium of Oidium in dormant buds. The results show that a specifi
c detection of Oidium mycelium is possible without visualizing other f
ungal mycelia in dormant buds of grapevines.