Problem of cactus

Question

I’m Turkish. I couldn’t find the answer In my country. I’m sorry if I can’t write it correctly. I’m unhappy because my cactus has a problem.
There’s a problem with the Opuntia vulgaris.A microorganism is eating Top of the its head. If it wants to grow up, it looks like a heart because the Hill can’t grow. It infected my cactus with the new Cactus. My cactus was good.
I added a photo for example.What’s the name of the problem? What’s the name of this virus? help me please:(
thank you very much

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Answer 1

It appears to be a leaf spot fungus. The best thing to do is remove the damaged area and discard. The wound should callus over.

https://www.gardeningknowhow.com/ornamental/cacti-succulents/prickly-pear/prickly-pear-phyllosticta-fungus.htm