Leeks diseases and pests
The database lists 4 problems recorded on this crop. 2 of them can cost the whole harvest, and 2 survive in soil or debris into next season — those are the ones that decide your rotation. The largest number are active in March.
Pressure through the year
The number of problems listed as active in each month. Pick a month to see what to sow, plant and harvest then.
Start from what you can see
What actually prevents them
Water at the base of the plant in the morning, never over the leaves. Splashing soil onto foliage is the delivery route for every problem listed here, and morning watering lets anything that does land dry before nightfall.
Applies to: Rust
Mulch the soil surface. A physical barrier between last season's spores and this season's lowest leaves removes the first infection of the year, which is the one that seeds all the others.
Applies to: Rust
Give the plants their full spacing 15×40 cm and keep the centre of each one open. Air moving through the planting dries the leaves faster, and leaf wetness duration is what turns a spore landing into an infection.
Applies to: Rust
Rotate this bed and everything else in the same family on at least a three-year cycle. 2 of the problems below survive in soil or crop debris between seasons, so returning the same crop to the same ground hands them the host they were waiting for.
Applies to: Onion White Rot, Rust
Clear and remove the spent crop at the end of the season rather than digging it in. Debris left on the surface is where the persistent problems overwinter, and next spring they start from your own bed rather than from somewhere else.
Applies to: Onion White Rot, Rust
Keep affected material out of the compost heap — 1 of these survive a garden heap and come back with the finished compost. Bag it for municipal green waste, which is composted at temperatures a garden heap does not reach.
Applies to: Onion White Rot
Every listed problem
Ordered by how much they can cost you.
Fungal diseases(2)
- Onion White RotCritical
Leaves yellow and die back from the tips while the plant is still growing, and the whole plant lifts out easily. The base of the bulb is covered in a dense white, fluffy mat studded with poppy-seed-sized black sclerotia.
- How it spreads
- Soil and crop debris
- Compost
- Keep out of the compost
- Conditions
- 10–24°C · humidity ≥80%
- First move
- Remove affected material now
- RustModerate
Yellow, orange, or rusty-brown powdery pustules on leaf undersides with yellow speckling above; severe infection causes leaf drop and weakened plants.
- How it spreads
- Rain and irrigation splash
- Compost
- Hot compost only
- Conditions
- 10–24°C · humidity ≥85% · wet leaves / rain
- First move
- Treat, then re-check in 5–7 days
Also at risk: Beans, Garlic, Broad beans, Sweetcorn, Asparagus, Blackberries
Pests(2)
- Allium Leaf MinerSevere
A line of small white dots down the leaf, made by adults feeding, is the first sign. Larvae then tunnel down into the stem and bulb, where they pupate as brown rice-grain-shaped puparia. The plant distorts, rots and is usually unusable.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 8–25°C
- First move
- Treat, then re-check in 5–7 days
Also at risk: Garlic
- ThripsModerate
Silvery or whitish streaks and stippling on leaves and petals, tiny black faecal specks, distorted buds and flowers, and scarred fruit; slender insects that scatter when disturbed.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 20–35°C · dry air ≤60%
- First move
- Treat, then re-check in 5–7 days
Why rotation matters here
2 of these overwinter in the soil or in crop debris rather than on the plant. Pulling the sick plant does not remove them: they wait for the same host to come back to the same ground.