Inhibitory effect of nonionic surfactants on sunflower downy mildew. A quantitative structure–activity relationship study

The inhibitory effect of 21 nonionic surfactants (nonylphenyl and tributylphenyl ethylene oxide oligomers, sorbitan derivatives) on the ontogenetic life cycle of sunflower downy mildew fungus (Plasmopara halstedii Farl. Berlese et de Toni) was determined and the strength and selectivity of the inhibitory effect was separated by using spectral mapping technique. It was established that surfactants exert no marked influence on living zoosporangia but inhibit the other forms. Calculations indicated that both the strength and selectivity of the effect of surfactants considerably depend on the length of the polar ethylene oxide chain and the hydrophobicity of the surfactant molecule has a secondary importance. Surfactants with medium length of ethylene oxide chain were more toxic than surfactants with very short or very long ethylene oxide chain.