Abstract: Pythium oligandrum is a newly biopesticide which shows great effects against many kinds of plant diseases. In greenhouse experiment, we found that Pythium oligandrum had different suppressing effects on cucumber downy mildew following different application time. The result showed that the control effect of Pythium oligandrum on cucumber downy mildew reached 68.9% when applicating the biopesticide Pythium oligandrum before cucumber downy mildew occurred. In comparison, the control effect only reached 23.5%, and the cucumber downy mildew had occurred seriously. It is better to apply Pythium oligandrum before or in the early stage of downy mildew pathogenesis occurring for better disease control.

Key words: Pythium oligandrum, cucumber downy mildew, control effect