Losing my crop

I'm a Brit living near Carcassonne in France and cannot find a good supply so have returned to growing after 30 years absence. I currently have three plants, all budding nicely, but one has been struck by a fast acting leaf thing. It started yesterday. The photo attached will show the leaf starts to go golden brown at the tip then it follows the edges and joins up pretty soon making the leaf curl. She's looking very sad today after I sprayed her with 60% mancozèbe (Dithane) but not much worse. Anyone got any ideas? I'd hate to lose her.

Hey sponge, you got a Phosophorus(P) deff. I suggest lower pH to 6-7(clay soil), 5.5 - 6.5 soils, Add complete fert with phosophorus. An excess of Fe and Zn in acidic soil makes Phosophorus unavailable. Flush / lower pH to either one of those 2, clay/soils.

Thanks Joel, will try that but why are the other two plants not in the same state? They get the same treatment. Sponge