# Pre-harvest interval in onion growing: how we plan the last treatments

Pre-harvest interval in onion growing: how it differs from the re-entry period, why it alone does not mean zero residues, and how we plan the last treatments.

The pre-harvest interval is the number of days from the plant protection product's label that must pass between the last treatment and harvest. Observing it is a legal duty and, when the product is used according to the label, it is meant to ensure that residues stay below the permitted level. It does not promise zero. That is why in our onion growing the label's pre-harvest interval is a lower limit, not a plan: we build in a margin for the last treatments ahead of the harvest date, we cut weed chemicals with spot spraying, and we check the effect in the laboratory on every batch.

## Pre-harvest interval, re-entry period and MRL: three terms that get confused

Before we describe how we do it, we set the terms straight, because in conversations with buyers these three terms often blur together.

| Term | What it means | Who it protects |
| --- | --- | --- |
| Pre-harvest interval | minimum number of days from the last treatment to harvest, given on the product label | the consumer, by limiting residues in the crop |
| Re-entry period | the time after a treatment during which people may not enter the field and animals may not be let in, and for some products a separate bee re-entry period also applies | workers, bystanders and pollinating insects |
| MRL (maximum residue level) | the legal limit for residues of a given substance in a given product | the market: a batch above the MRL cannot be sold |

The pre-harvest interval is set so that once it has passed, residues stay within the MRL when the product is used according to the label. That is an important caveat: the interval does not promise that the laboratory will detect nothing. It is meant to ensure that, when the product is used according to the label, any level detected stays within limits. We explain the difference between "within limits" and "below the limit of quantification" in more depth in our post [pesticide-residue-free onion or organic](/blog/cebula-ekologiczna-czy-bez-pozostalosci).

## Why the pre-harvest interval is harder in onions than in cereals

Onions have a long season and keep an open soil profile through most of the summer, so weed and disease pressure lasts almost until harvest. The most demanding period is just before the leaves fall over: the onion is still maturing and can still be exposed to leaf diseases, while at the same time every treatment at this point moves closer to the edge of the interval.

Then there is the weather. Onion harvest is not a date on the calendar, but the moment the leaves fall over, which a wet or dry summer can shift by weeks. If we plan the last treatment right at the edge of the interval and the field matures faster, we are left waiting until the interval passes, even at the cost of onions held too long in the field. That is why we keep a bigger margin between the last treatment and the expected harvest than the label requires.

## How we plan the last treatments before harvest

We grow according to the principles of Integrated Plant Production, and that changes the way we think about a treatment: we apply it when it is justified, that is after scouting the field, a pest or disease warning, or a damage threshold being crossed. What this method involves, we describe in our post on [Integrated Plant Production](/blog/integrowana-produkcja-roslin). In practice it looks like this:

- **We count back from harvest, not forward from the treatment.** For every field we estimate when the leaves will fall over and build the programme so that the last treatment has a margin above the label's pre-harvest interval. When the weather forces a later treatment, we choose the product with the shortest interval, push back the harvest of that field, and test the batch before dispatch just the same.
- **We choose a product for its interval, not only for its efficacy.** Of two products with similar action, late in the season we choose the one with the shorter interval, so that the safety window is wider.
- **We limit weed chemicals with spot spraying.** The [Ecorobotix ARA](/blog/ecorobotix-ara-oprysk-punktowy) sprayer uses cameras to spot weeds in a 6 by 6 centimetre grid and applies the product only where a weed is growing. That cuts chemical doses by around 70 percent, and less substance in the field means less substance that would have to break down before harvest.
- **We record every treatment.** Keeping records of plant protection treatments is a duty under EU Regulation 1107/2009 and must be kept for at least three years. For us it is also a planning tool: looking at a field's record card, we can see straight away when a given field can safely be harvested.

{% callout tone="warning" %}
A margin above the pre-harvest interval is not a luxury, it is insurance against the weather. An onion that matured a week earlier than we expected has to be ready for harvest, because the pre-harvest interval for every treatment on that field has already passed. If it is not, the whole harvest plan for that field falls apart.
{% /callout %}

## Harvest and curing: what happens after the last treatment

After the leaves fall over we lift the onions and lay them in windrows, where they dry in the field, and then for 2-4 days we cure them in the store with warm air. This stage is not about residues, but it is connected to them: between the last treatment and dispatch, not only does the pre-harvest interval pass, but also the time lying in the windrow and curing, so the real gap before a batch reaches the buyer is longer than the interval alone. What the harvest looks like, we describe in our post [harvesting onions with a combine step by step](/blog/zbior-cebuli-kombajnem-krok-po-kroku).

{% captionedImage src="/images/video/wyorywanie-cebuli-detal.webp" alt="The Grimme windrower undercuts the onions and lays them in windrows to dry in the field" caption="Harvest only starts once the pre-harvest interval has passed, and in a normal season with a margin above it." /%}

## Batch testing: we check instead of assuming

The interval, the choice of products and spot spraying are the plan. The proof is the laboratory result. We test every batch for pesticide residues, heavy metals and substances hazardous to health, and the goal is not to stay within the MRL, but a result below the limit of quantification, that is, the lowest concentration a laboratory can reliably measure. What exactly we test for and what the document for the buyer looks like, we describe in our post on [pesticide residue testing](/blog/badania-pozostalosci-pestycydow).

For packing houses and processing plants this is a concrete benefit: the batch history from us (field, treatment dates, pre-harvest intervals, test result) is documented and we make it available at the request of the buyer or an auditor. We pass the batch test results along with the produce. We produce using a technology free of pesticide residues, in line with the principles of Integrated Plant Production, and that claim in our offer stands behind exactly this chain: field observation, treatment only when justified, a margin above the interval, spot spraying and testing every batch. We show the whole growing process from sowing to harvest in our guide [onions from Żuławy: how we grow them](/blog/cebula-z-zulaw-jak-uprawiamy).

If you are looking for onions with documentation you can show your own customers, take a look at our [onion offer](/oferta/cebula) and write to us through the [contact form](/kontakt). The price is calculated from current market prices, and we pass the batch test results along with the produce.

## Frequently asked questions

### What is the pre-harvest interval in onion growing?

It is the minimum number of days between the last plant protection treatment and harvest, given on that product's label. It is mandatory and set so that, when the product is used according to the label, residues after it has passed stay within the maximum residue level (MRL), but it does not mean they are zero.

### How does the pre-harvest interval differ from the re-entry period?

The pre-harvest interval protects the consumer and counts down to harvest. The re-entry period protects people, animals and pollinating insects, and it sets how long after a treatment you may not enter the field or let animals in, and for some products also when the treatment is safe for bees. These are two different periods from the same label.

### Does observing the pre-harvest interval mean there are no residues?

No. The interval is set so that, when the product is used according to the label, the result stays below the MRL, that is, legal, but not necessarily zero. We aim for a result below the limit of quantification, which is why we keep a margin above the interval, cut doses with spot spraying, and test every batch.

### How can you check whether an onion supplier observed the pre-harvest interval?

Ask for the field's record card with treatment dates and the batch's residue test result. Treatment records are mandatory and must be kept for at least three years, so a reliable grower has them on hand. With us that batch history is documented and we make it available at the request of the buyer or an auditor.

### Why does spot spraying matter for residues?

Because the Ecorobotix ARA applies the product only to the weed, not to the whole field, and cuts doses by around 70 percent. Less substance in the field means a lower risk that anything remains in the onion by harvest.