Courgettes: Pests & Diseases
Courgettes are fast, generous plants for a sunny UK plot, though their large leaves and rapid growth can conceal trouble. They need fertile soil, regular water and plenty of space. Young plants are vulnerable to molluscs, while later crops often face mildew and pollination difficulties.
Common pests
Slugs and snails are the main early threat, eating seedlings and young leaves overnight. Aphids may colonise shoot tips and can transmit cucumber mosaic virus. Red spider mite and whitefly occasionally affect plants under cover, but are less common outdoors. Vine weevils may damage container-grown roots. Bees are allies rather than pests, as they are essential for reliable pollination of outdoor flowers.
Common diseases
Powdery mildew is common from late summer, covering leaves with white powdery patches and weakening plants. Cucumber mosaic virus causes mottled, misshapen foliage and distorted fruit, usually after aphid activity. Grey mould can affect damaged flowers and fruit in wet, crowded conditions. Poor pollination, especially in cool or wet weather, causes small fruit to yellow and rot at the tip without a spreading disease.
Prevention
Plant after frost risk has passed into fertile, moisture-retentive soil, allowing at least 90 cm between plants. Rotate cucurbits around the plot and clear old crop debris at season's end. Water at soil level in the morning and mulch to keep moisture even. Use horticultural fleece over young plants until established, removing it when flowering begins. Choose varieties noted for disease resistance where available.
Non-chemical control
Hand-pick slugs and snails at dusk, remove hiding places and protect seedlings with physical barriers. Rub off small aphid colonies or wash them away with water, while encouraging hoverflies, lacewings and ladybirds. Remove leaves badly affected by mildew to improve airflow, without stripping the plant. Remove rotting, poorly pollinated fruit promptly. Avoid handling wet foliage, which can spread disease between plants.
What to look for
Inspect seedlings daily for mollusc damage during their first few weeks. From flowering onwards, check beneath leaves weekly for aphids and white mildew patches. In cool, wet spells, examine young fruit for yellowing or rot and look for a shortage of insect activity around open flowers.
Tips
Harvest courgettes when young and tender, every few days, to keep plants productive. Water generously in dry weather but avoid sudden flooding after drought. If pollination is poor, hand-pollinate early in the morning using freshly opened male flowers.
Courgettes pests & diseases: frequently asked questions
What are the common pests of courgettes?
Slugs and snails are the main early threat, eating seedlings and young leaves overnight.
What diseases affect courgettes?
Powdery mildew is common from late summer, covering leaves with white powdery patches and weakening plants.
How do I prevent pests and diseases on courgettes?
Plant after frost risk has passed into fertile, moisture-retentive soil, allowing at least 90 cm between plants.
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.