NEED ASSISTANCE ASAP - What’s eating my cacti and how do I treat

[misteek]

Hey everyone I have a massive problem and I don’t know where to start.
 

I’ve so far lost more than one plant to this simply by not paying attention to my cacti.

 

Seems to be some sort of of cacti borer which is eating the middle core of cacti.. No signs of pests but black marks have appeared in the side of one (suggesting some sort of fungal? Issue).

 

its seems to have eaten the core of 4 plants OVERNIGHT!

 

if anyone can assist in educating me on what this is and how to treat that would be fantastic.

 

Thanks SAB fam,

 

Edited December 8, 2025 by misteek
Add photos

[wachumacallit]

Bite marks at the tips remind me of snail damage. Not sure about the black stuff, but probably related to humidity as well. I'd make sure they get plenty of sunlight and ventilation. Snail damage nothing fatal, it'll heal. But I'd keep an eye on that black stuff, it may need to be surgically removed (or not).  

Edited December 8, 2025 by wachumacallit

[misteek]

FOUND THE CULPRIT! I hadn’t even thought of snails as I have mixed golden maifan into the soil but turns out it was just a hungry caterpillar!

 

He had gone for the soft light green or white tissue on the new growth.  

So covered in more golden maifan (just in case a hungry snail gets the same idea) and will check the edge of containers in a regular basis.

 

Thanks to all that responded and those I I pm’d before wachumacallit came to the rescue!

 

Yeah I’ll keep an eye on the black stuff and when we have some sunny days I’ll probably just cut it out as suggested.. I know it can do a lot of damage from a book I read.

 

Thanks again! Here’s a photo of the culprit (he couldn’t move haha)

[misteek]

Does anyone know what the Bunnings equivalent is of golden maifan? 
 

And I should probably cut the tops off these guys hey? Sorry I’m still a bit shocked that this type of damage could be done by a caterpillar 

Edited December 8, 2025 by misteek
Caterpillar talk

[wachumacallit]

I often just leave them to heal, they'll often start pupping from the damaged tip, which tends to look more natural than if they are cut with a knife. Depends on your aesthetic preferences. For fungal infections I usually wait and see - if the plant is healthy and there's enough biomass/energy in reserve, they can survive infection. You'd want to monitor it carefully, to see if it's spreading. Or you can cut them all nice and clean, that definitely sends a chemical trigger to produce new pups. Never seen a caterpillar that large near my cactus plants. Must be some huge mother moth. Never heard of golden maifan, sounds expensive. 

[Starward]

Just let them heal, they will scar over and throw out new pups. Nothing to worry about.

 

At worst you may want to cut the tips at a slight slopping angle, so that water does not collect in the tops and cause rot.

 

But i would not bother.

 

Edited December 8, 2025 by Starward

[teamwhy]

On 12/8/2025 at 3:40 PM, Starward said:

cut the tips at a slight slopping angle, so that water does not collect in the tops and cause rot.

 

This. you got to remember that these can grow to metres tall and any weird weak points can cause trouble down the track.