Actually using an ax frill with point source introduction of selective
herbicide one can selectively cull unwanted plant species.  The only real
problem might arrise if the plant is clonal and often the species within an
area can have root grafts which will allow the herbicide to spread killing
trees in a group when only an outerr one was targeted.
 
Frill the tree or sapling leaving a very unclean ax frill, sprqay in the
mixture of roundup, or other herbicide to thouroughly soak the area
limiting runnoff.  Allow it to stand and the roundup will be translocated
to the roots and kill the unwanted tree/shrub.  This can be very effective
and actully reduce the amount of herbicide that would be used in a
broadcast spray.
 
Check Journal of arboriculture for further info.  This was popular in the
seventies and is probably still in use in right-of-ways and for culling
woodlot trees.
 
Mike
 
>One oldtime beekeeper I know said that he didn't like
>Roundup because of the collateral root kill damage to surrounding
>trees/shrubs that he wanted. He used something called
>"blue vitriol" or "Prussic acid" by dipping his machete or
>a knife in the substance and cutting the bark of the tree.
>He said it worked slowly but surely and got rid of undesired
>trees/shrubs. Does anyone know if there are problems with
>this? I'd canvass/information gather before doing it
>myself.
>for what it's worth- Phil Wood