When is the last time pesticides may be applied before the harvest?

The correct choice is associated with the concept of the Pre-Harvest Interval (PHI), which refers to the minimum amount of time that must pass between the last application of a pesticide and the harvesting of the crop. This is established to ensure that pesticide residues do not exceed safe levels at the time of harvest, thus protecting consumer health.

Understanding the PHI is crucial for anyone involved in the application of pesticides, as it directly informs them of safe practices in relation to the timing of pesticide applications. By adhering to the PHI guidelines, pesticide applicators can enhance food safety and ensure compliance with agricultural regulations.

The other options do not align with the safety measures outlined by PHIs. Applying pesticides immediately before harvest could leave harmful residues, starting treatments at the onset of harvest does not provide an opportunity for residues to dissipate, and suggesting that applications can occur anytime during the growth period disregards the critical importance of timing in relation to harvest and consumer health considerations.