There are 3 of this same cactus sharing the pot. Only one of them is getting these spots. What could it be? Fungus? Sun burn?
They are in my balcony, they don't get rain, and they get like 3-4 hours of direct sunlight in the morning. Not 100% but I think that the one with the spots was facing back (ie: facing the window) when it started.
What can I do to treat it?
- All cacti are 2 years old
- The "infected" one is around 25cm (10in) tall and 6cm (2.5in) in diameter.
- I've found the spots about 2 or 3 weeks ago, and I think they are spreading to a larger area of the cactus.