Downy mildew of cucurbits causes severe to devastating infestations on cucumber.
Scientific name: Pseudoperonospora cubensis
Greek name: Περονόσπορος Κολοκυνθοειδών, Ψευδοπερονόσπορος
On leaves it causes chlorosis in extensive angular areas between nerves. As the infestation progresses, the leaves dry out and fall off. Whole plants may also dry out. With favorable moisture conditions the white exanthem of the fungus, consisting of conidiophores and conidia, appears on the lower surface.
Pathogen – Growth conditions
The disease is caused by Pseudoperonospora cubensis. Cucumber greenhouses are particularly affected in autumn and winter. The fungus infects with zoospores from the leaf stomata in the presence of free moisture (water drops on the plant surfaces) for a certain period of time.
However, temperature is less of a determining factor because the fungus grows and infects over a wide range, even at lower temperatures, compared to other downy mildews.
It is difficult to deal with it once it has established in the greenhouse. Therefore, preventive spraying every week is recommended.