Downy mildew of Cucurbits
On the underside of the leave fluffy growth appears which is first white and later turns grey-brown. This is actually the sporulation of the pathogens extruding [...] stomata. Life cycle and appearance of Downy mildew Pathogens causing downy mildew are not fungi but Oomycetes and related to Pythium and Phytophthora. They [...] most downy mildews, the optimum temperature is around 15 o C and the closer the temperature is to this, the shorter the leaf wetness period that is required