Downy mildew: Difference between revisions
Created page with "'''Downy mildew''' is a serious fungal disease of the grapevine caused by the oomycete ''Plasmopara viticola''. It is one of the most significant threats to viticulture, affecting vine growth, fruit development and ultimately wine quality. The disease thrives in warm, humid conditions, where it can spread rapidly through vineyard canopies and severely reduce yields if not effectively controlled<ref>Robinson (ed.), ''The Oxford Companion to Wine'', 2015.</ref>..." |
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Latest revision as of 14:32, 14 September 2025
Downy mildew is a serious fungal disease of the grapevine caused by the oomycete Plasmopara viticola. It is one of the most significant threats to viticulture, affecting vine growth, fruit development and ultimately wine quality. The disease thrives in warm, humid conditions, where it can spread rapidly through vineyard canopies and severely reduce yields if not effectively controlled[1].
History and spread
Downy mildew is native to North America, where local vine species developed resistance to the pathogen. It was accidentally introduced into European vineyards in the late 19th century, carried on imported American rootstock[2]. The outbreak quickly spread across France, Italy and other parts of Europe, devastating traditional Vitis vinifera plantings. Today, the disease is present in most winegrowing regions worldwide, particularly in areas with significant summer rainfall or frequent morning dew[3].
Symptoms and identification
The first signs of infection appear as small, yellowish oil spots on the upper surface of vine leaves. Under humid conditions, these develop into white, downy fungal growth on the underside of the leaves[4]. As the disease progresses, leaves may brown, curl and drop prematurely, while shoots can become stunted and brittle. Infected grape clusters shrivel and may fail to ripen properly, rendering them unsuitable for winemaking. Because the symptoms resemble those of other vineyard diseases, careful monitoring and correct diagnosis are critical for effective management.
Viticultural impact
Outbreaks of downy mildew can drastically reduce vineyard productivity. Severe infections defoliate vines, reducing photosynthesis and weakening the plant’s reserves for future seasons[5]. Bunch infections lower yields and compromise grape composition, leading to musts with lower sugar content, unbalanced acidity, and higher susceptibility to spoilage during fermentation. In regions heavily affected, the disease has historically threatened the viability of viticulture itself.
Control and management
Effective control relies on an integrated approach. Vineyard managers often use canopy management to improve air circulation and reduce leaf wetness, which limits conditions favourable to the pathogen[6]. Fungicide sprays, especially copper-based treatments such as the Bordeaux mixture, remain a common preventive measure[7]. However, their use is regulated due to environmental concerns. The timing of applications is crucial, with protection needed around flowering and during periods of rain. Breeding programmes have also developed hybrid grape varieties with greater resistance to downy mildew, although such cultivars are less common in traditional European appellations.
Relation to wine quality
The presence of downy mildew can have a direct effect on wine quality. Grapes damaged by the disease may produce wines lacking aromatic intensity and structural balance[8]. Infected bunches are also more prone to secondary infections, including grey rot, which further deteriorate grape condition. By reducing the health of both leaves and fruit, downy mildew diminishes the ripening potential necessary for fine wine production. As a result, disease management is considered a cornerstone of maintaining consistent quality in both still and sparkling wines.
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, 2015.
- ↑ Jackson, Wine Science, 2020.
- ↑ OIV, “Plasmopara viticola (downy mildew)”.
- ↑ UC IPM, “Grape – Downy mildew”.
- ↑ Robinson (ed.), The Oxford Companion to Wine, 2015.
- ↑ Smart & Robinson, Sunlight into Wine, 1991.
- ↑ Jackson, Wine Science, 2020.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 2, 2006.