"Mike" wrote

Cover the holes into which you put the SBK with something removeable so
you
can give the holes another fill of the stuff from time to time.

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Will SBK kill the root? I know it will not do it toooooooooooo much good,
but I thought that SBK should be applied to leaves as it is systemic.

It will kill the root of a non conifer, yes, it's worked for me.
Conifers die just by being cut down so no green is left.

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Regards
Bob Hobden
17mls W. of London.UK