In organic cucumber production the infection with downy mildew (Pseudoperonospora
cubensis) is one of the major problems. Use of biological control agents based on
plant extracts and antagonistic micro organisms may be one possibility to control the
disease.
Plant extracts from Salvia officinalis and a plant belonging to the family Fabaceae
(P1), as well as cultures of Brevibacillus brevis showed, in bioassays on potted
cucumber plants, high potential to control the disease with efficacies between 55%
and 100%. For S. officinalis extract the efficacy was close to 100% even at a
concentration of 0.1325%. Initial trials under commercial growing conditions showed
that the control of P. cubensis is better in protected than in open field production. In
order to optimise the efficacy of the preparations for use in commercial cucumber
production, further investigations on the mode of action, the active ingredients etc. are
under way
