Dendrobium spots and eaten Phaius leaves

[Bloodygoose]

Help - I've been building a small collection of Australian native orchids in Melbourne for about a year - and I'm experiencing my first real pest and/or disease problems.

Some of the dendrobiums (speciosum and howeanum) are developing black spots, which is not scale.

I've also got a small Phaius Australis and some cymbidiums that are being attacked - the leaves seem eaten away. I pulled a small slug like creature off one leaf.

Some pics attached. I've tried spraying with mild pest and fungus spray but it hasn't made much diference. The attacks are growing.

Any help is appreciated. Ta.