kumquat - ours had a touch of what we assumed was orf last year. Seemed to be self-limiting. It was nowhere near as bad as some images of orf that we looked at and cleared by itself in a short time. We did try spraying the purple stuff on them but it seemed to irritate them, they rubbed their heads on the ground and made it worse

so in the end kept a close eye on them and applied vaseline as a barrier (fly season) to a few of the worst affected. They had been nibbling thistles so maybe something to do with that and not orf ..... who knows .... but it passed very quickly.