Has it gotten worse? Is it soft & mushy? If it is, I recommend cutting away the damage, spraying it with a peroxide/water mix 50/50 the dealing the wound with cinnamon. Only water the roots and try to keep your leaves dry.

Thanks Carlota. I wasn't sure if I should have cut off the whole pseudobulb. I just cut off the leaf. The black spot hasn't appeared elsewhere on the plant. All my orchids except "baby" ones stay outside all year normally so I haven't been watering at all because we're in the peak of the rainy season right now. Honestly I've never treated any orchid for disease. I don't even fertilize. I'm a bad gardener lol. My orchids are in lava rock. But there's always lizard, frog and bird droppings around so I guess they get fed. Lol

!I'm really happy to hear it hasn't spread! Ahhh... You're a fuss-free gardener! I try hard to be fuss-free but I'm not dry zone 10, it's a challenge. Your climate is perfect for many orchids. Lol, you now have my recipe for treating diseases. Rain water is full of lovely nutrients for your chids .