Under moist conditions, the pathogen sporulates on the affected tissues and spreads to other plants, on the leaves and stalks of which it forms greyish-violet local lesions.

[4] The symptoms begin as elongated, pale yellow lesions which progress into small patches of fungal colonies that are gray in color.

[8] During the summer, oospores induce hyphal growth into the leaf tissue of the onions, in which sporangiophores emerge.

[9] The sporangiophores then release sporangia, which are most often spread by wind, in which the pathogen may be capable of traveling several miles before reaching a new host plant.

As the season ends, Peronospora destructor overwinters in leaf debris as mycelium, and in the soil as oospores.

[9] The disease of downy mildew as a whole is most likely to grow on plants that are in cool and damp environments, however, the pathogen has different ways of utilizing environmental factors depending on the condition.

For example, if the host plant is in a rainless region, morning dew may create conditions that are suitable for downy mildew to grow.

[7] Rainless regions in which Peronospora destructor is found include Saudi Arabia, Iraq, Lebanon, Libya, and Turkey.

Fungicides such as dithiocarbamates, chlorothalonil, copper, ametoctradin/dimethomorph, and fenamidone may be applied to plants when early symptoms are present.

Throughout the growing season and after harvest, removing plant debris can be helpful in preventing the spread of P.