What are the methods of reducing vortex?
Wing vortices  cannot be reduced. It is a byproduct of creating lift. The various wingtip shapes help to combine the airflow from the top and bottom of the wing and can make the wing act like it is longer and creating the same lift, but the vortex is still generated. The biggest vortices are created by the big airplanes when they are heavy, dirty (lots of flaps, etc. deployed) and slow (i.e. takeoff and landing).  Even my little 4-seat Cessna Cardinal creates vortices.

See Section 3.14 here
http://www.av8n.com/how/htm/airfoils.html#sec-vortices
of this great e-book "See How It Flies"
http://www.av8n.com/how/