Buckthorn has a fibrous root system so not likely to graft into orher roots. For trunks under 2.5 inches in diameter you could rent or buy a weed wrench if you are leery of herbicides.

tj

.but what if the buckthorn roots are intertwined with the roots of good trees that I want to keep, could those trees be harmed as well?

==>>> NO

no need to paint either.. use the container at link... trust me.. its a lot cleaner than hoiking around a brush dripping with killer ...

fill with stump killer of any kind.. and apply to the green rim of a cut plant .. the cambium layer...

it has to be a fresh cut...

i use round up undiluted.. as it is labeled as such for a stump killer ...

im right handed.. killer in applicator in left hand.. pruning shears oi right hand.. snip and drip and snip and drip.. ad nauseum ...

close container and store in garage until next spring...

ken

https://duckduckgo.com/?q=plochman+yellow+mustard&t=ffsb&iar=images&iax=images&ia=images

Thank you, @tsugajunkie z5 SE WI ♱ and @ken_adrian Adrian MI cold Z5!

We have Round-Up as well as Triclopyr, the latter of which I just used to get rid of a patch of poison ivy, which I am extremely allergic to. I am okay with using herbicides in cases such as that and with buckthorn.

Well I guess I’ll have to have hubs recut some of the stumps so I have fresh wood to apply the herbicide to. Much of the buckthorn are established trees, but I’ve been on a rampage ripping out the numerous seedlings that pop up everywhere and anywhere. In one of our forested areas, the buckthorn outnumbered the good trees by 5:1. Nasty, nasty, things!!

Yeah, best to start with the biggest/oldest first to stop the seeding and move down from there.

tj