🧅 Onion How hard it is to control: ★★★★☆ 4/5

Neck rot on onion

Botrytis allii infects onions in the field through the neck as they dry off, but the symptoms only show after several weeks in store. It is the main cause of onions rotting in storage.

Symptom photos

Neck rot — Onion cut in half — whole surface covered in grey mould — Onion cut in half — whole surface covered in grey mould Photo: Gerhard Bedlan, Univ.Doz. Dr, licence CC BY-SA 4.0

Neck rot — Onion scale — grey-black clusters of spores and small sclerotia — Onion scale — grey-black clusters of spores and small sclerotia Photo: Jerzy Opioła, licence CC BY-SA 4.0

Symptoms

Watery, grey-brown rot starting at the neck
A grey, dusty bloom of spores between the scales
Small black sclerotia on the surface of the scales
Bulbs soft and sunken when the neck is squeezed
Symptoms showing after 4-8 weeks in store

What it does to the crop

Onions rotting in store, often whole batches
Losses appearing long after harvest
Neighbouring bulbs in the crate becoming infected
No way to save an affected bulb

What encourages it

Rainy weather while the crop is ripening and being lifted
Lifting onions that are not dry enough
Too much nitrogen and a thick, fleshy neck
High humidity in store

Prevention

Stop nitrogen feeding by the middle of the growing season at the latest
Lift only after the necks have died down naturally
Dry the onions thoroughly in an airy place before storing
Store at 0-2°C and 65-70% humidity
Do not cut necks too short while the tissue is still green

⚠️ Before you reach for a spray

This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.

Keep the disease atlas with you in the garden

In the app you can identify a disease from photos, work out the spray dose for your own bed and log the treatment in your task calendar. Free, no sign-up, works offline.

Open the atlas in the app →

📅 When to Sow Onion? →