The PHI recommends sufficient time for a pesticide to break down and a PHI-value is both crop- and pesticide-specific. Adhering to the PHI is important for a number of health-related reasons but also because Canada’s export customers strictly regulate and test for the presence of trace residues of pesticides.
An excellent summary of PHI for various pesticides in their various crops was posted by Saskatchewan Agriculture's Danielle Stephens in 2016 within their Crop Production News.
Finally, work towards "Keeping It Clean" so your grain is ready for export! More information about PHI and Maximum Residue Limits (MRL) is available on the Keeping It Clean site.