Willow tree bark problem - help please !

[dan at rocket.thenet.co.uk]

I have several willow trees that we cut this year, and all but one
have regrown well.  However, one is not doing so well, and in fact it
is a problem on only one side of the trunk, where the bark is a
greyish-silver colour.  No shoots will appear through this area of
bark.  Is it possible to do anything about this, and does anyone know
what it is?  Many thanks for a direct e-mail reply.