It's a good idea to keep the rootstock foliage around until the graft is fully established. In your case, someone has already trimmed it, and the Silberlocke looks like it's already the dominant plant. I'd cut the firma wood off.

How should I cut it and where? I'm assuming I'd cut it at an angle close to the intersection of where they meet?

when was it planted ... i suggest cutting it off in 3 years ...

as few extra leaves.. is just that much more energy generated ... lets get the understock trunk bulked up a bit ...

you are not thinking in tree years ... you are thinking in terms of your instant gratification ... chill on that ...

i think .. for next time... i would have planted it slightly tilted.. so the prized cultivar.. was more upright ...

there simply is not hurry.. when dealing with trees.. aka conifers ... its not like you will need a bucket truck to do the trimming in a year or two... lol ...

ken

Nick, yes, that is where I would cut. With a sharp pruning tool to make as clean a cut as possible.

In your second pic, there are two small bud pushes at the lower end of the rootstock. I'd cut it as Dean says but at the level of the second bud push up, leaving a good cm. The angle need only be enough to shed water but not to leave a long wound to heal (in fact the angle of the rootstock probably means it doesn't need a sloping cut at all). The small stump left will eventually be indistinguishable so don't cut too close to the graft as the redundant rootstock bark die-back may reach it.

Next year after the scion flushes completely and that new growth has hardened off, cut off the rootstock about 1/2" above the graft union. That scion is plenty large enough to take over the duty of being the dominant shoot - on its own.

Dax