Many thanks, Shot. I'd been using phosphate spray and drench as well but stopped because the leaves were clean. Suddenly, they weren't :-( You are probably correct about letting them dry. I must admit I've been lazy about watering.
I applied Agri-Fos last night and removed all the infected leaves. They got drenched this morning by that downpour, so they are good for the moment (fingers crossed). There's lot of new leaf growth, so I'm hopeful. Kinabulensis and graveolens look the cleanest. Kutajensis and zibithinus have really taken a beating.
Please keep in touch, if you don't mind. I'd love to compare notes as the trees get older. Are you planning to trellis yours?
Regards,
Scott