On 30/05/2017 08:16, Chris Hogg wrote:
On Tue, 30 May 2017 07:28:13 +0100, "Bertie Doe"
wrote:

Many thanks Chris, much appreciated. I note that the "copper sulphate and
lime mix, was developed in the Bordeaux region of France" - so there's the
connection.

There was also a Burgundy mix, copper sulphate neutralised with
caustic soda. Both were developed to combat fungal attack on grape
vines, but they were applied very generously, and over many decades
resulted in a build-up of copper in the soil. I'm not sure whether
that's the principal reason for all the various copper fungicides
being banned, but it was contributory. Cheshunt compound is copper
sulphate neutralised with ammonium carbonate.

Used sparingly I doubt it is that much of a problem. Used regularly on
the same crop in the same dry ground it gradually builds up which is
what caused them problems in France. I suspect plants tolerate copper
quite well so it is more a problem of contaminating groundwater.

All the copper based fungicides work by inhibiting certain enzymes that
are present in damping off, mildews and blight fungi.

--
Regards,
Martin Brown