Thank you.
How do I know what is causing these marks on my cactus?
+1
Thank you.
It's likely some kind of fungus. Check this out for more info: https://homeguides.sfgate.com/black-spots-cactus-37433.html
Barbara maybe this will give you some information that you need https://homeguides.sfgate.com/black-spots-cactus-37433.html
This looks like a fungal infection called Anthracnose or Black Spot Disease. Pinch off all the leaves that are showing these signs and treat with a copper based fungicide, though be careful with that if the plant is an outdoor plant because you don't want copper building up in the soil. There are a lot of people that report good success using Neem oil every 7 days until there is no more sign of the disease as well.
Is it a Christmas/Thanksgiving/Easter cactus or an Epiphyllum https://www.networx.com/article/10-facts-about-christmas-cacti your over watering it needs good drainage and completely dry between watering