I'm not entirely sure how an inorganic, naturally occurring chemical would be classified under 'organic' legislation? I still don't understand how salt can be described as organic - sodium chloride, not a carbon atom in sight. Surely the point of organic in the farming sense is that it's avoiding using man-made anti-fungals, insecticides etc.? Mostly because we don't know the impact on the entire ecosystem? Copper occurs naturally in the earth and in the human body. Agreed using huge quantities of it over an entire farm might impact on the natural balance of that farm. Using a few milligrams on a single nectarine tree will neither impact the ecosystem of that garden, nor on the person consuming the nectarines, nor on any insects pollinating the flowers.
I've not used it on potatoes because I've been lucky enough, so far, to avoid blight. But I have used it on tomatoes the one year I was fast enough to spot blight early. Otherwise I have had dismal tomato crops for the last four years, entirely due to blight. I will be doing my best to spray this year - otherwise I will have to pay for tomatoes that have been transported for miles (worse for the environment) and probably grown under cover in a heated, lit environment (also acceptable under organic guidelines but far worse for the environment).
When it comes to moral highground, it's always good to consider the entire picture - just following a set of guidelines doesn't necessarily give you that highground.
H