Volunteer Seedling Has Managed To Grow Into An Established Fir Tree.

Question

The root balls are now on top of each other. I have managed to reduce the 5 foot volunteer to a stump with many roots. Is there such a thing as a permanent liquid that I can paint on stump to stop it’s growth without damaging the fir tree? The stump is almost impossible to remove. There is no question that this volunteer will continue to grow and cause a huge issue .

Answer 1

There are stump killer products, but I am concerned as it goes down to the roots it might affect the main tree's roots, too. I suggest contacting your local extension agent or an arborist who has undoubtedly seen this before. 
https://www.gardeningknowhow.com/extension-search