Melons: Pests & Diseases
Melons are rewarding but demanding crops, normally grown in a warm greenhouse or polytunnel in the UK. They need steady warmth, careful watering and good ventilation to set and ripen sweet fruit. Pest problems build quickly under cover, so regular inspection is especially worthwhile.
Common pests
Red spider mite thrives in hot, dry glasshouses, producing pale speckling and fine webbing beneath leaves. Glasshouse whitefly leaves sticky honeydew and can develop into large colonies. Aphids distort young shoots and may spread viruses. Slugs can damage newly planted melons, while mice may nibble ripening fruit. Poor pollination is also common under cover when insects cannot reach flowers.
Common diseases
Powdery mildew makes white, floury patches on leaves, particularly where air is still and plants are stressed. Downy mildew causes yellow angular marks and greyish growth underneath. Grey mould may rot stems, flowers or fruit in humid conditions. Cucumber mosaic virus can cause mottled, distorted leaves and poor fruit. Uneven watering can also lead to fruit splitting or disappointing flavour.
Prevention
Use a sunny greenhouse or polytunnel, provide generous spacing and train plants so foliage remains open to air. Water the soil rather than leaves, preferably in the morning, and ventilate on warm days. Clean pots, tools and benches before planting. Choose compact, greenhouse-suited varieties where space is limited, avoid overfeeding with nitrogen-rich fertiliser, and rotate with unrelated crops if growing in greenhouse borders.
Non-chemical control
Remove infested shoot tips or wipe off small aphid colonies before they spread. Encourage or introduce biological controls such as Phytoseiulus for red spider mite and Encarsia for glasshouse whitefly where suitable. Hand-pollinate open female flowers with a soft brush if insect activity is low. Remove mouldy flowers, leaves and fruit promptly, improve ventilation, and use copper tape or other physical barriers against slugs.
What to look for
From planting, inspect leaf undersides twice weekly for mites, whitefly and aphids. Watch for pale stippling, sticky honeydew and curled new growth. As flowers open, check whether small fruits are setting. During humid weather, examine stems, spent flowers and fruit for grey mould, and note any white or yellow leaf markings.
Tips
Aim for fewer, better-ripened fruits rather than allowing every fruit to develop. Support heavy fruit in nets or slings, keep it dry and harvest when it smells sweet, colours up and yields slightly at the stem end. Avoid sudden swings between drought and heavy watering.
Melons pests & diseases: frequently asked questions
What are the common pests of melons?
Red spider mite thrives in hot, dry glasshouses, producing pale speckling and fine webbing beneath leaves.
What diseases affect melons?
Powdery mildew makes white, floury patches on leaves, particularly where air is still and plants are stressed.
How do I prevent pests and diseases on melons?
Use a sunny greenhouse or polytunnel, provide generous spacing and train plants so foliage remains open to air.
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.