Grapes: Pests & Diseases
Grapes can crop well outdoors in warm, sheltered parts of the UK and are especially reliable in a greenhouse or conservatory. Vines need sun, firm support and disciplined pruning to prevent a tangled canopy. Good ventilation and carefully spaced bunches are central to keeping fruit healthy as it ripens.
Common pests
Wasps can split or hollow ripe grapes, while birds peck outdoor bunches as sugar levels rise. Under glass, red spider mite may cause fine leaf speckling and webbing, and mealybug hides in stem joints and beneath bark. Scale insects may appear as fixed brown or pale bumps on stems. Aphids can also distort soft new shoots in spring.
Common diseases
Powdery mildew is the main grape disease, forming a whitish coating on leaves, shoots and berries, often even in dry conditions. Downy mildew causes yellowish patches and can develop in wet weather. Grey mould, or botrytis, rots crowded or damaged bunches, especially where humidity is high. Trunk and cane dieback can follow pruning wounds or poorly removed dead wood.
Prevention
Grow vines where leaves receive sun and air can circulate, and ventilate greenhouses daily in warm weather. Prune and train regularly to create an open framework, removing excess shoots and thinning congested bunches. Water at the base rather than wetting foliage. Clear fallen leaves and spoiled grapes promptly, clean pruning tools between plants, and choose varieties suited to outdoor UK growing or protected cultivation.
Non-chemical control
Use fine netting outdoors before bunches ripen, and bag individual bunches where wasps are persistent, ensuring airflow remains adequate. Remove damaged grapes immediately, as they attract wasps and grey mould. Hand-remove mealybugs and scale from small infestations, and rinse aphids from young shoots. Encourage predators around outdoor vines. In glasshouses, maintain ventilation and use biological controls appropriate to red spider mite where available.
What to look for
From bud burst, inspect young leaves for aphids and the first white powdery mildew patches. In warm, dry glasshouses, check leaf undersides weekly for red spider mite and webbing. As bunches swell and colour, look for wasps, bird damage, split berries and grey mould, particularly within dense clusters.
Tips
Prune grapes at the correct dormant season for the training system, as late cuts can bleed heavily. Keep fruiting shoots well supported and avoid overloading young vines. Harvest only when berries taste sweet, since grapes do not become sweeter after picking.
Grapes pests & diseases: frequently asked questions
What are the common pests of grapes?
Wasps can split or hollow ripe grapes, while birds peck outdoor bunches as sugar levels rise.
What diseases affect grapes?
Powdery mildew is the main grape disease, forming a whitish coating on leaves, shoots and berries, often even in dry conditions.
How do I prevent pests and diseases on grapes?
Grow vines where leaves receive sun and air can circulate, and ventilate greenhouses daily in warm weather.
General guidance for UK home gardens, focused on prevention and non-chemical control. The RHS or a local garden centre can help with tricky cases. Page updated 18 Sep 2026.