Hello, today when I checked cacties I saw problem on one of my cacties..
I don't know nothing about that..
I got this cactus before 3 days..
Can you tell me please what is this damage? What is cause? Sun, bugs, freeze, water?
Need I treating with insecticides, fungicides or not?
Is it dangerous for other cactuses in collection? Can it expand?
Pic:
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Thanks for help!