When does the wizard competion start in of Waverly place?

The Wizard competition in Wizards of Waverly Place doesn't have a specific start date, as it's a recurring event throughout the series. It's not a one-time tournament, but rather a series of challenges that the three Russo siblings have to participate in to determine who gets to keep their magical powers.

However, the most important competition, the one that decides who becomes the family wizard, happens in the series finale, "Alex vs. Alex".