Leeks: Pests & Diseases
Leeks are hardy, long-season alliums that provide welcome harvests from autumn into spring. They need fertile, moisture-retentive soil and room to develop sturdy shafts. Although resilient to cold, they benefit greatly from early protection against flying pests and from avoiding ground with a history of serious allium disease.
Common pests
Allium leaf miner tunnels inside leaves and stems, leaving pale mines and brown pupae; spring and autumn are the principal flight periods. Leek moth larvae mine foliage and can damage the growing point. Onion fly maggots may weaken young plants. Thrips cause pale streaks in dry weather, while stem and bulb eelworm can lead to twisted foliage and distorted stems.
Common diseases
Leek rust is common, showing as orange pustules that weaken foliage, especially in late summer and autumn. Onion white rot causes yellowing, decay, white fluffy fungal growth and black sclerotia around roots, persisting in soil for years. Downy mildew makes pale patches with greyish mould. Damping off affects crowded seedlings, and bacterial soft rots can enter damaged plants in wet conditions.
Prevention
Follow a long allium rotation and avoid beds where white rot has occurred. Raise healthy seedlings, space plants generously and water at soil level to improve airflow. Cover newly planted leeks with fine mesh or fleece during allium leaf miner and onion fly flight times, including spring and autumn. Remove old allium debris, clean tools and do not transfer soil between plots. Choose rust-tolerant varieties where available.
Non-chemical control
Keep fine mesh or fleece firmly sealed around young plants during pest flight periods. Remove leaves with heavy mining and dispose of seriously affected plants away from the compost heap. Hand-pick visible leek moth larvae where possible. Encourage birds, ground beetles and other predators with varied nearby planting. Remove rusted foliage if practical and improve spacing. For eelworm, destroy affected plants and avoid alliums in that soil for several years.
What to look for
Check leaves weekly from planting for pale mines, frass, brown pupae and small leek moth larvae. Look for silver thrips damage during dry weather. From midsummer, inspect foliage for orange rust pustules and mildew symptoms. Lift any plant that yellows or wilts unexpectedly, checking roots for white rot growth and black sclerotia.
Tips
Plant deeply or draw soil gently around stems to produce longer white shanks, but avoid burying leaf centres. Harvest as required in winter. Remove badly damaged outer leaves before bringing leeks indoors, and do not leave diseased plant remains on the bed.
Leeks pests & diseases: frequently asked questions
What are the common pests of leeks?
Allium leaf miner tunnels inside leaves and stems, leaving pale mines and brown pupae; spring and autumn are the principal flight periods.
What diseases affect leeks?
Leek rust is common, showing as orange pustules that weaken foliage, especially in late summer and autumn.
How do I prevent pests and diseases on leeks?
Follow a long allium rotation and avoid beds where white rot has occurred.
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.