Silencing tracks

I have a recording which is in stereo that I want to clean up. The problem is, the left had track of my intro has noise on it and should be silent [ruining the intro of the track. I want to know is it possible to silence that left hand section on a stereo track. i know how to generate silence on a stereo track but not singularly. I have attached a screen shot showing the track and that the bottom section needs to be silenced. Please can anyone help.

Probably the easiest way is to split the stereo track, then you can work on the two channels separately. See: