Q.Can My Cacti Be Saved?
I have neglected these cacti for 20 years (inherited from my mom after she died). The taller one seems to have a fungal infection? Is there anything I can do to save it? Same with the red button cactus. I notice some white patches that seem to be missing chlorophyll. both had lichen on it (mostly on the taller one). Can you also tell me what type of cactus the taller one is?
Certified GKH Gardening Expert
Make certain you are not overwatering. That is the surest way to harm a cactus. I don't see all of the tall plant, but it could be African milk tree (Euphorbia trigonia). Here are some articles that should help. (The milk tree may be overwatered or is getting too much sun) Lichen do not harm the plant.
https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/cactus-landscaping.htm
https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/fungal-lesions-on-cactus.htm
https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/erwinia-soft-rot-in-cactus.htm