Downy mildew refers to any of several types of
oomycete microbes that are
obligate parasites of plants. Downy mildews exclusively belong to
Peronosporaceae. In
commercial agriculture, they are a particular problem for growers of
crucifers,
grapes and
vegetables that grow on vines. The prime example is
Peronospora farinosa featured in NCBI-Taxonomy and HYP3. This pathogen does not produce survival structures in the northern states of the
USA, and overwinters as live mildew colonies in Gulf Coast states. It progresses northward with cucurbit production each spring. Yield loss associated with downy mildew is most likely related to soft rots that occur after plant canopies collapse and sunburn occurs on fruit. Cucurbit downy mildew only affects leaves of
cucurbit plants.