Study and careerWinemaking & vineyard
Vine diseases explained: fungal, bacterial, viral and phytoplasma
The main grapevine diseases by type: what causes them, how they spread, what they do to vines and wine, and how growers fight back. With a short quiz for wine students.
Updated October 2026
Rewritten by Alper Billik, Advanced Sommelier
5 min read
The short answer: grapevine diseases fall into four groups by cause. Fungal and fungus-like diseases, such as powdery mildew, downy mildew and botrytis, are the most widespread, and growers control them with sprays and canopy work. Bacterial diseases such as Pierce's disease, viral diseases such as leafroll and fanleaf, and phytoplasma diseases such as flavescence dorée can't be cured in the vine. Growers fight them by controlling the insects that spread them, planting clean vines and removing sick ones.
Fungal and fungus-like diseases
| Disease | Cause | Signs | Good to know |
|---|---|---|---|
| Powdery mildew (oidium) | The fungus Erysiphe necator | White-grey powder on leaves and berries; berries can split | Reached Europe from North America in the 1840s; sulfur is the classic treatment |
| Downy mildew | Plasmopara viticola, a water mould (oomycete), not a true fungus | Yellow 'oil spots' on leaves, white down underneath, damaged bunches | Recorded in Bordeaux in 1878; answered with Bordeaux mixture, copper sulfate and lime |
| Botrytis bunch rot (grey rot) | The fungus Botrytis cinerea | Grey mould on bunches in damp weather | In the right conditions the same fungus becomes noble rot, behind Sauternes and Tokaji |
| Black rot | The fungus Guignardia bidwellii | Brown leaf spots; berries shrivel into hard black mummies | Native to North America; worst in warm, wet seasons |
| Trunk diseases: esca, Eutypa and Botryosphaeria dieback | Wood-infecting fungi, often entering through pruning wounds | Dead arms, cankers; 'tiger-stripe' leaves with esca | No cure; careful pruning and wound protection |
- Powdery mildew (oidium)
- CauseThe fungus Erysiphe necator
- SignsWhite-grey powder on leaves and berries; berries can split
- Good to knowReached Europe from North America in the 1840s; sulfur is the classic treatment
- Downy mildew
- CausePlasmopara viticola, a water mould (oomycete), not a true fungus
- SignsYellow 'oil spots' on leaves, white down underneath, damaged bunches
- Good to knowRecorded in Bordeaux in 1878; answered with Bordeaux mixture, copper sulfate and lime
- Botrytis bunch rot (grey rot)
- CauseThe fungus Botrytis cinerea
- SignsGrey mould on bunches in damp weather
- Good to knowIn the right conditions the same fungus becomes noble rot, behind Sauternes and Tokaji
- Black rot
- CauseThe fungus Guignardia bidwellii
- SignsBrown leaf spots; berries shrivel into hard black mummies
- Good to knowNative to North America; worst in warm, wet seasons
- Trunk diseases: esca, Eutypa and Botryosphaeria dieback
- CauseWood-infecting fungi, often entering through pruning wounds
- SignsDead arms, cankers; 'tiger-stripe' leaves with esca
- Good to knowNo cure; careful pruning and wound protection
The Bordeaux mixture story is a good one for exams: the botanist Alexis Millardet published it in 1885, after noticing that vines sprayed with copper sulfate and lime, to put off grape thieves, had escaped downy mildew.
Bacterial diseases
| Disease | Cause | Signs | Good to know |
|---|---|---|---|
| Pierce's disease | The bacterium Xylella fastidiosa, spread by sharpshooter insects | Leaf scorch, wilting, and eventually a dead vine | Serious in parts of the Americas; Xylella is a priority quarantine pest in the EU |
| Crown gall | The bacterium Agrobacterium vitis | Tumour-like galls on the trunk, often after frost injury | Plant clean vines and limit winter damage |
| Bacterial blight (maladie d'Oléron) | The bacterium Xylophilus ampelinus | Cankers and dieback on young shoots | Spread on pruning tools and planting material |
- Pierce's disease
- CauseThe bacterium Xylella fastidiosa, spread by sharpshooter insects
- SignsLeaf scorch, wilting, and eventually a dead vine
- Good to knowSerious in parts of the Americas; Xylella is a priority quarantine pest in the EU
- Crown gall
- CauseThe bacterium Agrobacterium vitis
- SignsTumour-like galls on the trunk, often after frost injury
- Good to knowPlant clean vines and limit winter damage
- Bacterial blight (maladie d'Oléron)
- CauseThe bacterium Xylophilus ampelinus
- SignsCankers and dieback on young shoots
- Good to knowSpread on pruning tools and planting material
Viral diseases
| Disease | Cause and spread | Signs | Effect on wine |
|---|---|---|---|
| Leafroll | Leafroll-associated viruses, spread by mealybugs and soft scale insects, and by infected cuttings | Leaves roll downwards and turn red in black varieties in autumn | Slower, uneven ripening, less colour |
| Fanleaf degeneration | Grapevine fanleaf virus, spread by the dagger nematode Xiphinema index | Deformed, fan-shaped leaves; poor fruit set and shot berries | Much smaller crops |
| Red blotch | Grapevine red blotch virus | Red blotches on the leaves of black varieties | Delayed ripening; first noticed in California in 2008, the virus identified in 2012 |
| Rugose wood | A group of viruses, mostly spread through infected planting material | Pitted, grooved wood under the bark | Weaker vines, lower yields |
- Leafroll
- Cause and spreadLeafroll-associated viruses, spread by mealybugs and soft scale insects, and by infected cuttings
- SignsLeaves roll downwards and turn red in black varieties in autumn
- Effect on wineSlower, uneven ripening, less colour
- Fanleaf degeneration
- Cause and spreadGrapevine fanleaf virus, spread by the dagger nematode Xiphinema index
- SignsDeformed, fan-shaped leaves; poor fruit set and shot berries
- Effect on wineMuch smaller crops
- Red blotch
- Cause and spreadGrapevine red blotch virus
- SignsRed blotches on the leaves of black varieties
- Effect on wineDelayed ripening; first noticed in California in 2008, the virus identified in 2012
- Rugose wood
- Cause and spreadA group of viruses, mostly spread through infected planting material
- SignsPitted, grooved wood under the bark
- Effect on wineWeaker vines, lower yields
Phytoplasma diseases: grapevine yellows
Phytoplasmas are tiny bacteria without cell walls that live in the plant's sap-carrying tissue (the phloem) and travel in sap-sucking insects. The diseases they cause are grouped as grapevine yellows. Leaves turn yellow (white varieties) or red (black varieties) and curl, shoots fail to turn woody, and bunches shrivel.
- Flavescence dorée: spread vine to vine by the leafhopper Scaphoideus titanus, introduced to Europe from North America. It is an EU quarantine disease: where it is found, insecticide treatment and the uprooting of infected vines are compulsory.
- Bois noir: caused by 'Candidatus Phytoplasma solani' and spread mainly by the planthopper Hyalesthes obsoletus, which lives on weeds such as bindweed and nettle. Managing those weeds is part of the defence.
- Telling them apart: the symptoms look the same, so only a lab test can say which one it is.
Not a disease: phylloxera
Phylloxera is an aphid-like insect that feeds on vine roots. From the 1860s it destroyed vineyards across Europe. The lasting answer was grafting European vines onto resistant American rootstocks, which is why grafted vines are the norm in Europe today.
How growers protect their vines
- Airflow and canopy: open canopies dry fast after rain, and dry leaves resist mildew and rot.
- Timely sprays: sulfur against powdery mildew, copper against downy mildew, plus modern products, timed to the weather.
- Clean planting material: certified, virus-tested vines are the main defence against viruses.
- Vector control and roguing: controlling the insects and removing infected vines before they spread disease.
- Careful pruning: clean cuts at the right time and protected wounds against trunk diseases.
- Resistant varieties: newer disease-resistant grapes, called PIWI in German-speaking countries (from *pilzwiderstandsfähig*, fungus-resistant), need fewer sprays.
Diseases are one reason a crop can be small; the weather at flowering is another: see coulure and millerandage. For why some grapes are so hard to grow, read why Pinot Noir is a diva.
Quick quiz
Question 1
What causes downy mildew?
- a)Erysiphe necator, a fungus
- b)Plasmopara viticola, a water mould
- c)Xylella fastidiosa, a bacterium
- d)A virus spread by mealybugs
Show answerAnswer
b) Plasmopara viticola, a water mould. Plasmopara viticola is an oomycete, a fungus-like water mould. Erysiphe necator causes powdery mildew.
Question 2
Which disease is spread by sharpshooter insects?
- a)Pierce's disease
- b)Black rot
- c)Leafroll
- d)Esca
Show answerAnswer
a) Pierce's disease. Sharpshooters carry the bacterium Xylella fastidiosa from vine to vine.
Question 3
What spreads grapevine leafroll virus in the vineyard?
- a)Dagger nematodes
- b)Mealybugs and soft scale insects
- c)Wind
- d)Pruning shears only
Show answerAnswer
b) Mealybugs and soft scale insects. Mealybugs and soft scale insects, as well as infected planting material. Dagger nematodes spread fanleaf.
Question 4
Flavescence dorée is caused by:
- a)A fungus
- b)A virus
- c)A phytoplasma
- d)An insect
Show answerAnswer
c) A phytoplasma. A phytoplasma, spread by the leafhopper Scaphoideus titanus.
Question 5
Which fungus causes both grey rot and noble rot?
- a)Botrytis cinerea
- b)Guignardia bidwellii
- c)Erysiphe necator
- d)Eutypa lata
Show answerAnswer
a) Botrytis cinerea. Botrytis cinerea: destructive in damp weather, precious when misty mornings give way to dry, sunny afternoons.
Question 6
What is phylloxera?
- a)A fungal disease
- b)A virus
- c)An insect that attacks roots
- d)A bacterial disease
Show answerAnswer
c) An insect that attacks roots. An aphid-like insect. Grafting onto American rootstocks is the lasting answer.
Questions people ask
What are the most common grapevine diseases?
Powdery mildew, downy mildew and botrytis bunch rot are the ones most growers have to manage every season.
Can a vine with a virus be cured?
No. Viruses, phytoplasmas and bacteria such as Xylella stay in the vine. Growers plant clean material, control the insects that spread them and remove infected vines.
Is phylloxera a disease?
No, it's an insect that feeds on the roots. Vines are protected by grafting them onto resistant American rootstocks.
Do vine diseases affect the taste of wine?
Yes. Rot can bring mouldy, off flavours, and viruses such as leafroll and red blotch delay ripening, giving less sugar and colour.
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