Don't forget that wingtip vortices are generated in all normal phases of flight, including landing. They are present on approach all the way through the landing, but are most severe prior to the main wheels touching down. Due to relatively large flap deflections involved in landing, vortices can be generated even at the low angles of attack and relatively low airspeeds of the landing roll out. As an interesting aside, I have often heard vortices overhead just short of the approach end of an active runway at MIA. They make a sound akin to the tearing of paper or light fabric, such as a sheet. Of course, the vortices can actually be seen on humid days.
Cheers,
Grog