Your BG will out spawn them and they will naturally have a smaller influence in the future. But I would pull them now to keep the BG genes as pure as possible. In the future, I would use them as bait if I found them and your LMB are big enough to eat them.

I have been pulling ours and using them as bait for a few years. Our pond is five years old.

Hope this helped.

Brian

The one thing is the one thing
A dry fly catches no fish
Try not to be THAT 10%