Viticulture
The diseases that matter
Powdery and downy mildew, grey rot, trunk diseases, leafroll virus and Pierce’s disease — what each does and why it shapes where wine is grown.
The short answer
A handful of diseases account for most of what shapes viticulture: two mildews that arrived from North America in the nineteenth century, grey rot, a group of fungal trunk diseases, several viruses, and a bacterial disease that makes viticulture impossible in parts of the Americas.
Overview
Disease pressure explains more about the world wine map than climate alone does. Humid regions grow different varieties, train them differently and spray more.
This page is informational. It describes what these diseases are and why they matter for wine; it is not a grower’s spray guide and gives no treatment recommendations.
Why it matters in the glass
Disease pressure is why cool-humid regions favour open canopies and disease-tolerant varieties, why organic viticulture is much harder in the Loire than in Mendoza, and why hybrid varieties persist despite their exclusion from many quality designations.
Step by step
1 Powdery mildew (oidium)
A fungus attacking green tissue and berries, causing splitting and off-flavours. Arrived in Europe in the 1840s from North America. Does not require free water, so it affects dry regions too — which distinguishes it from downy mildew.
2 Downy mildew (peronospora)
Arrived in Europe in the 1870s, carried on phylloxera-resistant American rootstock imports. Requires warmth and moisture, and it is why humid regions have such high disease pressure. Bordeaux mixture — copper sulfate and lime — was developed against it and is still permitted in organic viticulture.
3 Grey rot (Botrytis cinerea)
The same fungus as noble rot, behaving destructively. On intact healthy grapes in the right conditions it concentrates sugar; on damaged fruit or in persistently wet weather it destroys the crop and introduces laccase, an enzyme that oxidises wine aggressively.
4 Trunk diseases (esca, eutypa, botryosphaeria)
A group of fungal infections that colonise the permanent wood, gradually killing the vine. There is no effective cure once established, and the withdrawal of sodium arsenite has left growers with limited options. A serious and growing economic problem in mature vineyards worldwide.
5 Leafroll and fanleaf virus
Viral diseases spread by mealybugs and by nematodes respectively, and by infected propagation material. They reduce yield, delay ripening and lower sugar accumulation. Certified virus-tested planting material is the principal defence.
6 Pierce’s disease
A bacterium spread by sharpshooter insects that blocks the vine’s water-conducting tissue and kills it, usually within a few years. It makes Vitis vinifera viticulture effectively impossible across much of the southeastern United States and is a standing threat in California.
In history
Sources
Sources consulted
- UC Davis Department of Viticulture and Enology — University of California, Davis
- INRAE — French National Research Institute for Agriculture, Food and Environment — INRAE
- The Australian Wine Research Institute — AWRI
More in the vineyard
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Climate and wine style
The largest single influence on what a wine tastes like — larger than grape, producer or winemaking, and the reason the same variety is unrecognisable in two places.
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Climate change and wine
Warming is already reshaping where wine is grown and what it tastes like.
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Harvest and picking decisions
When to pick — the single most consequential decision a producer makes each year.