I have a cactus that’s 19 yrs old. It has white bumps on it and spikes coming out of the bumps. A gardenia tree next to the
cactus also has the white bumps on its branches, but no spikes coming out of the bumps. What is this?
It sounds like you may have a Scale infestation.
Isolate the plants so it does not spread further.
Neem Oil is a good treatment for these pests.