What is this?

[Bolero]

I probably should know but have never seen this in any of my plants.......only a couple are affected but they are fairly rare hangianum hybrids so I want to save them if I can.

Will it spread? How do I treat these plants? None of the plants around them are affected so far. I have only had them a month or so and have been watering about twice a week.

Any advice would be greatly appreciated.

Darren