Powdery mildew
Powdery mildew (also known as oidium) is one of the most widespread fungal diseases affecting vines, with significant impact on grape quality and wine production. It is caused by the pathogen *Erysiphe necator*, a fungus that thrives in warm, dry conditions and can severely reduce yields and compromise wine quality if not controlled.[1]
Background
The disease was first identified in Europe in the mid-19th century, having been introduced from North America. It spread rapidly through the vineyards of France, Spain, and Italy, causing widespread crop loss until the adoption of sulphur treatments offered effective control.[2]
Today, powdery mildew remains a constant threat in viticulture worldwide, from Europe and the Americas to Australia and South Africa.
Characteristics
Powdery mildew manifests as a white, powdery coating on leaves, shoots, and grape berries. Infected leaves may curl or become distorted, reducing photosynthesis, while affected berries may split, shrivel, or fail to ripen properly. Severe infections can impart unwanted flavours and aromas to wine, often described as mouldy or earthy.[3]
The fungus does not require free water for infection, unlike downy mildew, and can develop rapidly under moderate temperatures and high humidity. Spores overwinter in vine bark and buds, allowing early-season infections that spread throughout the growing cycle.
Management in Viticulture
Control of powdery mildew relies on a combination of cultural, chemical, and biological methods. Key strategies include:
- Canopy management to improve airflow and reduce humidity.
- Sulphur sprays, historically the most common treatment, remain widely used.
- Fungicides and integrated pest management approaches tailored to vineyard conditions.
- Resistant varieties and rootstocks, though limited in traditional wine regions.
Regular monitoring and early intervention are critical, as severe outbreaks can devastate yields and reduce both the ageing potential and sensory quality of wines.[4]
Impact on Wine
Powdery mildew affects both yield and grape composition. Infected berries often show reduced sugar accumulation, altered acidity, and diminished colour in red varieties. Wines made from infected grapes may lack balance and display off-flavours. For this reason, significant infection is typically considered unacceptable in quality-focused production.
See also
References
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020 (vineyard diseases). ISBN 978-0128161180.
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015 (entry: oidium/powdery mildew). ISBN 978-0198705383.
- ↑ UC IPM, “Grape—Powdery Mildew”. https://ipm.ucanr.edu/agriculture/grape/powdery-mildew/
- ↑ OIV, “Vine health—powdery mildew resources”. https://www.oiv.int