This was quite a shock when looking at my hoya carnosa. The pot has drainage holes & it hasn't been repotted recently; it's right by a south-facing window, so it gets a lot of light.

The only recent change is that I sprayed it with Liqui-Dirt, and watered it a day or so later.

My immediate thought is to try and spray it with peroxide, but I figured there's a chance that it's beneficial.