There is some debate about the PHI for 2,4-DB based on wording on labels. I have often used 45 days as the PHI. The PHI is in reference to harvesting and not digging. One company is encouraging farmers to not spray 2,4-DB after the first of July because of residue concerns in the EU market. I often recommend sequential applications of 2,4-DB with fungicides to suppress escaped Palmer amaranth and sicklepod in fields.