affected by metalaxyl-M in oomycetes (Viranyi and Oros, 1991),
were strongly inhibited. The same was true for dimethomorph, a
fungicide which was expected to influence cell wall formation
during encystment and germ tube formation. This effect on
zoospore discharge is contradictory to the results of Albert et al.
(1991) who reported that dimethomorph inhibited all stages in
the developmental cycle of Phytophthora infestans and Plasmopara
viticola except zoosporangiogenesis, zoospore discharge and
motility. All three tested fungicides had inhibitory effects on the
germination of encysted spores. Particularly for azoxystrobin we
observed that the ED50 was significantly lower on germ tube formation
(0.1 mg/mL) when compared to the two earlier stages
(0.5 mg/mL).