Pre-harvest interval — the number that decides whether your produce sells or gets rejected

Every label has a line stating how many days before harvest you must stop spraying. The official term is the pre-harvest interval; many farmers simply call it the "waiting period".

Where does this number come from?

From trials of how quickly that substance breaks down in that crop until the remaining residue is below the accepted limit. The number therefore differs by substance and by crop. The same substance used on different crops may need different waiting periods.

Why it matters directly to your wallet

Export buyers, processing factories and modern retailers routinely test for residues. Produce that fails is not just rejected for that lot; it often gets you removed from the supplier list altogether, which costs many times more than the price of a single lot.

The most common mistakes

Spraying again close to harvest because pests have come back, when there are only a few days left before harvest. That spraying barely helps the yield any more, but it puts the whole field at risk of failing the standard.

Another case is harvesting in several rounds, such as vegetables picked every two or three days. In this case, count the waiting period from the last spraying of that field, not from the previous harvest round.

Write it down, do not rely on memory

The most effective way is to record every spraying date in a notebook or take a photo, along with the product name and the field sprayed. When harvest time comes you can answer straight away when the last spraying was. This record is also something buyers in certified systems already ask to see.

Drone spraying and record keeping

Drone spraying jobs have the advantage that the system records the date, time and area automatically, so you can look back at which field was sprayed on which day, which is exactly the information you need to answer questions about the waiting period.
Important note
This article explains general safety principles. It is not a recommendation to use any particular chemical. Mixing rates, the crops a product may be used on and the waiting periods required differ by product and change with government notifications. Always treat the product label as the authority, and consult an agricultural specialist or our staff before deciding to use it.