Plasmopara viticola, the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil.

[5] Plasmopara viticola, also known as grape downy mildew, is considered to be the most devastating disease of grapevines in climates with relatively warm and humid summers.

[6] Shortly after this first observation, the pathogen was introduced to European countries where it played a devastating role in the yield and production of their grapes, and consequently their wine.

Within just a few years of the pathogen's introduction the French attempted to graft American root stock to their own vines in order to produce a more resistant strain of grape.

[1] Because of numbers and results like these, downy mildew has been considered the most devastating disease of a filamentous pathogen to affect European vineyards.

Studies in Sicily have shown optimum time for oospore germination is between the end of February and the middle of March.

[4] With this understanding, if fungicides are used just before optimum conditions occur, they have proven to be an effective control method of the pathogen.

Other control methods include proper watering, and a good location where the plant can receive continual sunlight.

Oospores are the sexual structures resulting from the fertilization of oogonia by antheridia, that typically occurs in late summer.

The pathogen can survive winter as oospores in host tissue like dead leaves on the vineyard floor.

[8] The sporangia, seen as the white fungal-like organism on the downside of the leaves, are produced after a warm and high humid night.

Early in the season (spring), Yellow circular spots with oily appearances is going to present on foliage along with the veinlets.

As the oil spots age and develop, infected tissue would become necrotic and nonreproductive, due to cell death.

[5] If under appropriate weather conditions, a larger number of oil-spots can develop, expand, and cover most of the leaf surfaces.

After a warmer and humid night, a white downy fungal growth (sporangia) would be abundant on the downsides of the leaves and other infected plant areas.

After a warm humid night, these oily patches may also sporulate and be covered with white fungal growth.

[8] The disease development of grape downy mildew is known to be heavily reliant on the efficiency of the asexual propagation cycles.

Kiefer et al. (2002) demonstrated that the early development of Plasmopara viticola is regulated specifically and coordinately by unknown factors originating from the host grapevine plant Vitis vinifera.

The expressions of PR-2, PR-3 and PR-4 genes are induced in the grapevine host during pathogen infection, which encode for cell wall-degrading enzymes B-1,3-glucanase (PR-2) and chitinases (PR-3 and PR-4).

[14] In addition, the upregulation of the PR-9 gene that encodes for peroxidase, which is a reactive oxygen species is associated with the systemic acquired defense of the grapevine host.

PR-5 is involved in the synthesis of thaumatin-like proteins and osmotins, which are believed to inhibit the spore germination and germ tube growth of Plasmopara viticola by creating transmembrane pores.

[16] In order to prevent passersby from eating from grapevines close to the road, Pierre-Marie-Alexis Millardet sprayed those vines with a mixture of copper sulfate and lime, which was both seeable and awful-tasting.

[16] He then noticed that the treated grapevines did not show any symptoms of downy mildew, whereas the rest of the vineyard was infected by the disease.

[16] After further studies, Millardet published the recommended treatment of the grapevines against the downy mildew in 1885 in which he proposed the use of 8:15:100 of copper sulfate: hydrated lime: water mixture in the treatment (later named as Bordeaux mixture after the Bordeaux region where Millardet conducted the research).

[6] Another example is the cultivar Chancellor in which the leaves exhibit moderate levels of resistance to downy mildew, while the clusters, tendrils and shoot tips are highly susceptible to the disease.

[6] Several new European cultivars such as Regent have been developed from progeny of crosses between V. vinifera and resistant North American species in an effort to incorporate the most desirable qualities of both parental branches.

Canopy management practices, such as low planting density, vine trimming, and hedging, and later shoot thinning, can improve the air movement and make the leaves drier.

[19] Biological agents, like Epicoccum nigrum link, can inhibit the spread of spores of Plasmopara viticola.

[21] In 1848, Berkeley and Curtis made reference to a downy mildew on grapevines, and, in a footnote, named it Botryis viticola.