Be warned that Citrofresh is NOT cheap.
It's about a tenner a litre for the ready to use stuff, which I have my doubts about - best to get the concentrate and dilute it to a suitable strength I reckon. The ready to use stuff seems to become less effective the longer its been opened, unlike the concentrate, so I can't help wondering if some contamination is taking place.
Just as well I got 5L of concentrate as I've just discovered the place I bought it from seems to have ceased trading
Actually if you want to give the Citrofresh a try then PM me - I'm sure I can find a suitable container to send you some. The concentrate is used at 10:1* for active infections and 25-50:1 for barrier protection (which is where Citrofresh really excels) so I wouldn't have to send you that much really
It doesn't specifically mention blackspot on the container but if it can deal with fusarium, septoria and target spot I'd think blackspot could be treated too. Worth testing before shelling out for the concentrate (which only comes in 5L containers) perhaps.
*I've gone to 7.5:1 before for really bad infections