Arabica coffee plant

Coffee rust, or coffee leaf rust, first destroyed Brazil's crop in 1970. Since the occurance of coffee rust in Brazil, it has spread to every coffee growing country in the world. Coffee rust and its symptoms were first observed in Sri Lanka in the 1860's. Many countries, including Sri Lanka and Ethiopia, replaced much of their arabica coffee with disease resistant robusta coffee. Coffee leaf rust is spread by wind and rain from spores from lesions on the underside of the plant (Mitchell, 84).

The rust diesease in coffee is prevented by spraying with copper-based fungicides at 3-5 kg/ha at 4-6 week intervals during the rainy season

I'm guessing your plant is in a greenhouse/conservatory - do you get any coffee beans from it? I'd love to see a picture if possible :-) Sorry, can't help with your problem - just curious!