# Onion neck rot and other storage diseases: how we avoid them

Onion neck rot ruins batches only once they are in storage. We show where it starts, how we limit it in the field and at harvest, and what the sorter rejects.

Neck rot is the most treacherous onion disease there is: a batch looks healthy at harvest, rolls into the store healthy, and a few weeks later starts going soft from the top. The fungus behind it infects the plant back in the field and only shows symptoms in storage. We sell onions from our own 13 000 tonne store for most of the year, so we fight storage diseases not from November but from May. Here is how we do it.

## Where neck rot comes from

The culprit is a fungus of the genus Botrytis. It enters the plant through the neck, most often late in the season when the tops collapse, and through any wounds. It thrives on a wet summer, on harvesting immature onions and on a thick, unclosed neck that stays an open gate into the bulb for a long time. In storage the disease develops slowly and quietly: we usually find the first rotten bulbs after 4-8 weeks in the pile, and an infected onion goes soft from the neck down and turns grey under the skin.

The worst part is that at harvest the infection is practically invisible. That is why storage diseases cannot be "fought in the store". There you can only find them and sort them out.

## Three diseases that spoil onions in storage

| Disease | What gives it away | What favours it |
| --- | --- | --- |
| Neck rot | softening from the neck, grey mould under the skin, symptoms after 4-8 weeks | a wet end of season, immature harvest, a thick neck |
| Bacterial soft rot | single scales going soft, a sour smell, bulbs that feel "hollow" | harvest damage, rain before harvest, poor curing |
| Fusarium basal rot | rot starting from the base, white mycelium on the bottom of the bulb | infected soil, a warm season, no crop rotation |

All three share one thing: they are decided in the field and at harvest, long before anyone opens the storage door.

## Prevention starts in spring

The first line of defence is agronomy. We keep a crop rotation so soil-borne pathogens do not build up on the same plots. We watch our [nitrogen fertilisation](/blog/nawozenie-cebuli-azot-i-siarka): an over-fertilised onion builds a thick, juicy neck that refuses to close, and such a neck is an invitation for Botrytis. We run crop protection by the rules of Integrated Plant Production and test every batch for pesticide residues, so we cannot and do not want to throw chemicals around. All the more important that the plant matures evenly and manages to close up before harvest.

## Two-stage harvest and curing make the difference

We harvest onions in two stages: first a windrower lifts them and lays them in windrows, where the goods finish drying in the field, and only then do we pick them up from the windrows. This seemingly old-fashioned step is the most effective treatment against storage diseases we know: sun and wind close the necks and dry out the route the fungus takes into the bulb.

{% captionedImage src="/images/video/wyorywanie-cebuli-detal.webp" alt="Machine lifting onions and laying them in a windrow in the field" caption="Lifted onions go into windrows: this is where their storage resilience begins." /%}

After coming in from the field, the batch still goes through [2-4 days of curing](/blog/dosuszanie-cebuli-przed-przechowywaniem) in a stream of warm air. Only dry, closed onions travel on to their final place, where we hold them at a stable [0-2°C and 65-75 percent humidity](/blog/w-jakiej-temperaturze-przechowywac-cebule). Cold will not cure an infected bulb, but it slows the fungus down and stops it jumping to neighbouring onions.

## What the sorter catches, and what batch checks catch

No prevention gives you one hundred percent, which is why the [DOWNS CropVision optical sorter](/blog/sortownik-optyczny-downs-cropvision) stands between our store and the pallet. AI-assisted cameras look at every onion through 360 degrees and reject defective bulbs, including those with signs of rot, at up to 100 tonnes per hour. On top of that we check batches while they sit: better to find a problem in a chamber in December than on a customer's ramp in March.

{% callout tone="success" %}
The effect of this chain is simple: in February the buyer gets a batch that looks like an autumn one. We describe the whole process from field to dispatch in our post on [storing onions](/blog/przechowywanie-cebuli).
{% /callout %}

## What the buyer gets out of it

Storage diseases are the main reason for complaints in the winter onion trade. Buying from a farm that stores and grades its own goods, you get a batch screened for defects and checked while it sat, not goods with an unknown history. Check our [onion offer](/oferta/cebula) or describe what you need via the [contact form](/kontakt): we will share sizes, packing and dispatch dates from the store.

## Frequently asked questions

### Why do onions rot from the neck?

Most often it is neck rot caused by the fungus Botrytis, which infected the plant back in the field, through an unclosed neck or wounds. Symptoms only appear after a few weeks of storage, which is why the batch looks healthy at harvest.

### Can you see neck rot at harvest?

Practically not. Infected bulbs look normal and firm, and the disease usually shows itself after 4-8 weeks in storage. That is why field prevention, thorough curing and batch checks during storage are key.

### How do you prevent onion storage diseases?

The basics are crop rotation, restraint with nitrogen, harvesting mature onions, curing until the neck closes and stable, cool conditions in the store. The last line of defence is grading, which rejects defective bulbs before packing.

### Can diseased onions be sorted out of a healthy batch?

To a large extent, yes. The optical sorter rejects onions with visible symptoms, and batch checks in the chambers let us catch an outbreak early and route the batch to faster sale or extra grading.