Posted: 15/09/2015 at 20:51
I would try it on one of them first and see what happens. We used Roundup painted on to the leaves. It may take a fair while to deal with all of them and it is better not to do them all at once, that might give the tree a fatal shock.
Obviously avoid getting the stuff on the grass though.
As for the ones in soil, then yes go for the old fashioned method. Find the root where the sucker emerges and rather than cutting it off, try to scoop out the point of origin, say about a tea-spoon depth into the old root. Not easy, I know. You need a good strong sharp knife to do it.