Every pesticide label carries a number that many farms ignore until a buyer rejects a load: the pre-harvest interval, or PHI. It is the minimum number of days between the last spray and harvest, so that residues fall below the safe limit.
Why it matters
- Food safety: vegetables and fruit are often eaten fresh. Residues above the limit are a health risk.
- Buyers and exports: supermarkets, processors and export buyers test for residues. One failed test can cost a contract.
- Your name in the mandi: traders remember whose produce caused problems.
Reading the label
Look for "pre-harvest interval", "PHI" or "days to harvest". Typical values range from 0 to 3 days for some fungicides, 7 to 14 days for many insecticides on vegetables, and 21 days or more for some products on cotton or orchards. The label for the crop you are spraying is the one that counts.
The label may also give a re-entry interval in hours: how long workers should stay out of the sprayed field.
Working out the safe date
Safe harvest date = spray date + PHI days. A spray on 24 September with a 21-day PHI means no picking before 15 October. If the field gets a second spray, the later safe date wins.
Keeping track on a busy farm
The problem is rarely knowing the rule; it is remembering it for twenty fields when the picking crew is ready. A few habits help:
- Write the safe date on the field board or in the field group the day you spray.
- Tell the munshi and the picking contractor, not just the spray team.
- Check the last spray before every picking, especially in tomato, chilli and other multi-pick crops.
In FarmOS, entering the PHI with each spray sets the safe-to-harvest date automatically. The dashboard lists fields that cannot be harvested yet, the farm map shows a red "do not harvest before" date on the plot, and recording a harvest inside the interval shows a warning.