Swiss Chard: Pests & Diseases
Swiss chard is a colourful, productive leaf crop that supplies tender leaves and crisp stems from spring into autumn, and often through winter in mild areas. It is hardier and generally less prone to bolting than spinach. Give it a sunny or lightly shaded bed, fertile soil and room to develop large plants.
Common pests
Mangold fly, or leaf miner, is the principal pest, creating blistered tunnels between leaf surfaces and spoiling young leaves. Aphids can gather on new growth and beneath leaves, leaving sticky deposits and distorted foliage. Slugs chew holes in seedlings and low leaves during damp weather. Pigeons may peck small plants or newly planted rows. Caterpillars occasionally nibble foliage, though established chard often tolerates modest feeding without any noticeable reduction in cropping.
Common diseases
Leaf spot can produce brown, grey or purplish lesions that enlarge and make leaves unattractive for harvesting. Downy mildew causes yellow patches with greyish growth beneath leaves in cool, wet conditions. Damping-off and root rots affect seedlings in poorly drained soil. Grey mould may develop where old leaves are left wet and crowded. Bolting can occur after stress, but chard is usually more reliable and less bolt-prone than spinach.
Prevention
Rotate chard away from spinach and beetroot, especially if leaf spot or downy mildew has been troublesome. Start with clean seed, sow into well-drained soil and thin plants to at least 30 cm apart for airflow. Choose sturdy varieties suited to year-round harvesting. Water at the base, remove damaged outer leaves regularly, and keep the bed free of decomposing debris. Fine mesh over young crops helps prevent leaf miner and bird damage.
Non-chemical control
Remove mined leaves while the tunnels are small, before mangold fly larvae leave to pupate in soil. Use fleece or fine mesh over seedlings and newly planted crops, securing edges well. Hand-pick slugs after dusk and provide habitat for beetles, frogs and birds that feed on them. Rub off aphid colonies or remove heavily infested leaves, allowing hoverfly larvae and ladybirds to work. Dispose of badly spotted foliage away from the plot.
What to look for
Inspect new leaves weekly from spring for mangold fly eggs, pale mines and aphid colonies. Check seedlings after wet nights for slug grazing. During prolonged damp weather, look under leaves for downy mildew and examine older foliage for expanding leaf spots. Watch central stems in warm weather for early signs of bolting.
Tips
Harvest outer leaves individually, leaving the crown intact for months of regrowth. Smaller leaves are mildest, while thick stems suit cooking separately. Protect overwintering plants with fleece during severe cold, and remove faded leaves to keep plants clean and productive.
Swiss Chard pests & diseases: frequently asked questions
What are the common pests of swiss chard?
Mangold fly, or leaf miner, is the principal pest, creating blistered tunnels between leaf surfaces and spoiling young leaves.
What diseases affect swiss chard?
Leaf spot can produce brown, grey or purplish lesions that enlarge and make leaves unattractive for harvesting.
How do I prevent pests and diseases on swiss chard?
Rotate chard away from spinach and beetroot, especially if leaf spot or downy mildew has been troublesome.
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.