This document describes several genera of oomycetes that cause downy mildew diseases in plants. It provides details on their taxonomic classification, structures and life cycles. Key points include: - Plasmopara viticola causes downy mildew of grapes and produces both asexual zoospores and sexual oospores. - Pseudoperonospora cubensis causes downy mildew of cucurbits like cucumber and produces sporangia and infects via intercellular hyphae. - Bremia lactucae causes downy mildew of lettuce and has asexual sporangia and can reproduce sexually or asexually via oospores.