String control is something that is slowly developed throughout the time you play... it's not something you really sit and practice (or atleast most people don't)... It's something that at first you have to make sure you pay attention to until it becomes subconcious.

Try to mute the string that you most commonly sound when bending with one of your free fingers on your fretting hand... or possibly palm mute the string with you your pick hand. Those are two general ways to go about it. mess around with those two ways and see which one may work for you. It may feel uncomfortable at first but it should get easier as with everything else.