You must use Glyphosate sprayed onto the foliage in late summer/early autumn. This is the most effective time of year to apply as the plant will take the glyphosate sugars down into its roots through the leaves so killing it. Leave as much leaf surface as possible ie don't be tempted to cut it back or you will reduce the amount of glyphosate taken up by the plant.

It will still come back no matter what you do! But you can reduce it I dig mine out every time it comes through from my neighbours gardens.