Have not looked into this fully, but my RHS magazine pointed out that Dithane fungacide has been made illegal & that the recomended replacement is based on Copper Oxychloride.
Don't know if it's too diluted or adulterated, but might be worth a look...
Never had you pinned as green fingered Phil.
Is that there CuOCl any good for them blues? I have only used it as a catalyst so far (very good). I may give it a whirl when I get a chance.