Sweetcorn diseases and pests
The database lists 4 problems recorded on this crop. 0 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 June.
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 35×45 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: Corn Smut
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.
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.
Every listed problem
Ordered by how much they can cost you.
Fungal diseases(2)
- Corn SmutModerate
Silvery-white swollen galls on cobs, tassels, stems or leaves, which enlarge, darken and finally rupture to release a mass of powdery black spores. Infected plants may also be stunted or distorted.
- How it spreads
- Wind-blown spores
- Compost
- Hot compost only
- Conditions
- 26–34°C · dry air ≤60%
- First move
- Treat, then re-check in 5–7 days
- 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, Leeks, Garlic, Broad beans, Asparagus, Blackberries
Pests(2)
- CaterpillarsModerate
Ragged holes and chewed leaf margins, stripped stems, dark green or black droppings (frass), and tunnelled or bored fruit; large green or striped larvae present.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 15–33°C
- First move
- Treat, then re-check in 5–7 days
Also at risk: Cabbage, Kale, Broccoli, Cauliflower, Brussels sprouts, Kohlrabi
- CutwormsModerate
Young plants cut clean through at soil level and left lying beside the stump. Later in the season, surface grazing on potato tubers and carrot shoulders. Scrape the soil within a few centimetres of a felled plant and a fat grey-brown caterpillar curls up in a C shape.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 12–30°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.