Spring Onions: Pests & Diseases
Spring onions are fast, compact alliums suited to beds, containers and gaps between slower crops. Succession sowing gives tender stems over a long season. Their shallow roots need regular watering in dry spells, while mesh protection and clean crop rotation help prevent flying pests and persistent allium diseases.
Common pests
Onion fly maggots can tunnel into seedlings, causing sudden yellowing and collapse. Allium leaf miner makes winding mines, with brown pupae in leaves or stems; its main flights are usually spring and autumn. Thrips may cause pale, silvery streaks during dry weather. Leek moth can damage leaves, and stem and bulb eelworm may produce distorted, stunted plants with poor-quality stems.
Common diseases
Onion white rot causes wilting, rotting roots and bulbs, white fluffy fungal growth and small black sclerotia that survive for years in soil. Downy mildew causes pale yellow patches and greyish mould in damp conditions. Damping off can remove crowded young seedlings. Soft rots follow injury or waterlogging, while neck rot may affect any spring onions held too long after lifting.
Prevention
Sow in fresh ground on a long allium rotation and avoid any bed known to have white rot. Use clean seed, thin seedlings for airflow and avoid waterlogged soil. Cover rows with fine mesh or fleece through onion fly and allium leaf miner flight periods, particularly in spring and autumn. Keep paths and tools free of moved soil, clear crop debris promptly, and water the soil rather than foliage.
Non-chemical control
Use insect mesh or fleece with edges tucked into the soil to exclude onion fly and allium leaf miner. Remove collapsed, mined or rotting plants promptly and dispose of them away from compost. Hand-weed gently to avoid root injury. Encourage ground beetles and birds around the plot. For eelworm symptoms, remove all affected plants, clean tools and keep alliums out of that patch for several years.
What to look for
Examine seedlings twice weekly during warm spring weather for wilting, yellowing and collapsed centres. Check leaves for pale mines and brown allium leaf miner pupae, especially in spring and autumn. Look for thrips streaks in dry conditions and mildew after rain. Pull and inspect any poorly growing plant before symptoms spread along the row.
Tips
Sow short rows every two to three weeks for a continuing harvest. Keep plants evenly watered to prevent tough, sharp-tasting stems. Harvest young when stems are pencil-thick, and use them promptly for the best flavour and crispness.
Spring Onions pests & diseases: frequently asked questions
What are the common pests of spring onions?
Onion fly maggots can tunnel into seedlings, causing sudden yellowing and collapse.
What diseases affect spring onions?
Onion white rot causes wilting, rotting roots and bulbs, white fluffy fungal growth and small black sclerotia that survive for years in soil.
How do I prevent pests and diseases on spring onions?
Sow in fresh ground on a long allium rotation and avoid any bed known to have white rot.
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.