Wine · Grape Growing · Study guide
Pests & Disease
A study guide to the vineyard's above-ground threats — birds, mammals, mites and moths, and the fungal diseases downy mildew, powdery mildew and grey rot, plus IPM, spraying and canopy defence.
The vine's worst enemies live at the roots — phylloxera and nematodes, the subject of their own page — but plenty more attack it above ground. Animals eat the grapes, insects chew the leaves and fruit, and fungi — the real menace — rot the crop in a wet season. Against all of them the grower has a toolkit that runs from netting and predators to the spray tank, and the modern preference is to use the gentlest tool that works.
The framing idea: most vineyard threats are managed, not eliminated — and the smartest defence is often the vineyard itself. An open, airy canopy dries the fruit and starves fungi of the damp they need; encouraging a pest's natural predators can do the work of an insecticide. Learn which threat wants which conditions, and you can see the defence before you reach for a chemical. (Part of the Grape Growing library; the root pests are phylloxera & nematodes, and the philosophy behind low-spray farming is viticultural practices.)
The one thing to fix first: the canopy is a defence
Before any spray, the grower's most powerful tool against the biggest threat — fungal disease — is canopy management. Fungi need moisture and stagnant, humid air; an open, well-managed canopy lets air flow through and sun in, drying the fruit and leaves so the fungi can't get established. Get the canopy right and you spray less. Hold that idea — airflow is the first fungicide — and the rest is detail.
The threats at a glance
The memorise-cold table:
| Threat | What it is | Main defence |
|---|---|---|
| Birds & mammals | Eat grapes; damage brings rot and bacteria | Netting; fencing |
| Insects (spider mites, grape moths) | Feed on grapes and leaves | Insecticide; IPM (predators) |
| Downy mildew | Fungus of warm, wet (maritime) weather | Spraying (copper); open canopy |
| Powdery mildew | Fungus of warm, shady (not-humid) conditions | Spraying (sulphur); open canopy |
| Grey rot | Fungus of wet, humid weather, attacking grapes | Canopy, spraying; pick clean |
Key facts
| The root pests | Phylloxera & nematodes — their own page |
| The biggest above-ground menace | Fungal disease (mildews, rot) |
| The first defence | Canopy management — airflow and dryness |
| Animal defence | Netting (birds), fencing (mammals) |
| Insect defence | Insecticide, or better, IPM — natural predators |
| Fungal sprays | Sulphur (powdery), copper + sulphur (downy) |
| The catch on spraying | Must stop before harvest; heavy in maritime climates |
The vocabulary you'll actually meet
- IPM (Integrated Pest Management) — controlling pests by encouraging their natural predators and building biodiversity, rather than blanket spraying.
- Noble rot vs grey rot — the same fungus (Botrytis): benevolent (noble, for sweet wines) in the right dry-afternoon conditions, ruinous (grey rot) otherwise.
- Bordeaux mixture — the classic copper-and-lime spray against downy mildew (permitted even in organic viticulture, in limited amounts).
- Monoculture — wall-to-wall vines; IPM prefers biodiversity instead.
In this guide
- Animals and insects — netting, fencing, and IPM
- The three great fungal diseases, and the conditions each needs
- The threat → conditions → defence table
- Spraying and canopy — the two levers
- Classic exam questions
Animals and insects
- Birds and mammals. Birds strip ripening grapes, and mammals (deer, boar, rabbits) both eat fruit and damage vines; the wounds they leave invite rot and bacteria. The defences are physical: total netting of the vines against birds, and fencing against mammals.
- Insects. Smaller pests such as spider mites and grape moths feed on the leaves and fruit. They can be knocked back with insecticide, but the modern approach is IPM (Integrated Pest Management): instead of spraying everything, the grower encourages the pests' natural predators to live in and around the vineyard, building biodiversity rather than a sterile monoculture, and reaching for chemicals only when truly needed.
The three great fungal diseases
Fungi are the vine's most persistent enemy, and each favours particular weather — which tells you where it strikes and how to fight it:
- Downy mildew — a fungus that needs rainfall and warm weather, so it plagues maritime climates. It shows as yellow "oil spots" on the leaves and attacks the green parts of the plant. Fought with copper-based sprays (the classic Bordeaux mixture).
- Powdery mildew — thrives in warm, shady conditions and, unlike downy, does not need humidity. It attacks the young, green parts with a dusty grey coating. Fought with sulphur.
- Grey rot — needs rainfall and high humidity; it attacks the grapes themselves, causing colour loss and tainted flavours. It is the malevolent face of Botrytis — the very same fungus that, in dry-afternoon conditions, becomes the noble rot prized for sweet wines.
Threat → conditions → defence
| Threat | Conditions it needs | Defence |
|---|---|---|
| Downy mildew | Warm and wet (maritime) | Copper spray; open canopy |
| Powdery mildew | Warm and shady (not humid) | Sulphur spray; open canopy, sun |
| Grey rot | Wet and humid | Airflow, clean picking, spraying |
| Birds / mammals | Ripe fruit | Netting / fencing |
| Mites / moths | Warm season | IPM (predators); targeted insecticide |
The two levers: spraying and canopy
Spraying is the direct weapon. The two workhorse fungicides are sulphur (against powdery mildew) and copper (against downy mildew, often as copper + sulphur together). Two rules govern its use: maritime, rainy climates need far more spraying (the rain both spreads the fungi and washes the spray off), and all spraying must stop a set time before harvest so no residue reaches the wine.
Canopy management is the indirect — and often better — weapon. An open, well-arranged canopy improves airflow and lets sunlight in, so the fruit and leaves dry out quickly after rain and dew. Since every fungal disease needs moisture and stagnant air, a good canopy denies them the conditions they need, cutting the amount of spraying required. It's the cheapest, greenest fungicide the grower has — which is why the whole viticultural-practices movement leans on it.
Classic exam questions
- Which vineyard threats live at the roots, and where are they covered? — Phylloxera and nematodes — on their own page.
- How are birds and mammals kept off the crop? — Netting (birds) and fencing (mammals).
- What is IPM? — Integrated Pest Management — encouraging pests' natural predators and biodiversity instead of blanket spraying.
- Downy vs powdery mildew — conditions? — Downy needs warmth and wet (maritime); powdery needs warmth and shade, not humidity.
- What is grey rot, and its benevolent twin? — A humid-weather fungus that rots grapes; the same Botrytis becomes noble rot for sweet wines in dry conditions.
- Which sprays fight which mildew? — Sulphur for powdery, copper for downy.
- Why is canopy management a disease defence? — An open canopy improves airflow and drying, denying fungi the moisture they need — so you spray less.
Most of what threatens a vineyard is managed rather than beaten — and the grower who reads the weather and opens the canopy fights the battle before the spray tank is ever filled.