The preharvest interval (PHI) refers to the number of days that the crop should not be harvested after application of a pesticide. Harvest in this context means cutting or swathing. If the crop is harvested before the indicated interval has elapsed, there could be unsafe or unacceptable residues of the pesticide remaining in or on the harvested seeds.
Preharvest intervals are listed on the labels of pesticides and under the “Restrictions” section of individual product descriptions in a current provincial Guide to Crop Protection. When pesticide applications are being considered, take note of the required preharvest interval and allow for that time period before harvest.