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Thanks. Our spuds are doing so well....in buckets....I might just do some pre-emptive control.Bordeaux mixture (copper sulphate & calcium oxide) and Burgundy mixture (copper sulphate and sodium carbonate) have been used for many decades to prevent potato blight ie. best used pre-emptively rather than reactively. It was banned for amateur use about five years ago because, as far as I can tell, the copper can build up in the soil and harm earthworms. I have not managed to find evidence of harm to humans but I have asked the BMA to do a literature search. It is still used for spraying fruit trees. I have had scarcely any blight over several years so have not used the spray - so no danger of build-up in the soil. Both mixtures can still be purchased eg Vitax but now advertised as a mineral supplement for plant growth - JBM, do I remember that you use oxalic acid for cleaning the woodwork of your boat?
https://en.wikipedia.org/wiki/Burgundy_mixture
I've just looked up the Vitax copper mixture. Says it controls tomato blight too @pargyle