Pseudoperonospora cubensis is the scientific, Latin or binomial name for cucurbit downy mildew.

This particular fungus causes water mold in members of the gourd family (Cucurbitaceae). It first shows up as light yellow or green wounds on the foliage. It then further mars the appearance with gray to purplish-black fungal growths on the undersides of leaves. The dying leaves curl upward.

The rest of the plant - flowers, fruits, roots, stems - are unaffected directly. But there are indirect consequences from the lack of protection from the dying and dead leaves. Specifically, the unprotected fruit tends to end up misshapen or deformed.