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A year ago or so, my cactus started developing yellow spots all over and was diagnosed with a fungal infection. As instructed, I got an antifungal spray (copper-based) and was spraying it once a week or so. As far as the yellow spots go, I do not think it helped all that much. Still, the cactus was growing fine, so I did not worry too much. Eventually I gave up on that spray as it did not really make any difference.

That is, until I had a closer look at it a couple of days back and saw this:

cactus fungi

Now, I can clearly see at least two mushroom-like hyphae that are visibly macroscopic in size! Both seemed to be simply growing out of the soil next to the cactus. In fact, the largest one was impaled on it.

I removed the bits I could reach manually and sprayed the cactus again for the first time in many months. My questions now are:

  • Are those fungi just growing next to the cactus or are they feeding on it somehow with their roots (or whatever they have in place of roots)?
  • Is it likely that they are related to the fungus causing the yellow spots?
  • Have I done enough to get rid of them or do I need to do anything more extreme like replanting my cactus completely?

Thank you very much in advance!

Update: after removing the hyphae, an even bigger one grew out of nothing overnight:

Upclose

I wonder what species this is?

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Fungus in your cactus (desert cactus, anyway) indicates two possible conditions; you've got cactus growing in soil rich enough to support fungus (not a good thing), and you are probably over watering (ditto). In addition not enough airflow contributes to this situation.

For the fungus, I'd recommend finding some cactus/succulent soil and re-potting your plant with it, making sure there is adequate drainage. Cactus/succulent soil should not retain a lot of water, when you water it should run through and out the bottom of the pot quickly.

As for the yellow spots on the plant, those are also a fungus of some sort, I call it rust. It's presence indicates too much humidity and not enough airflow and/or sunshine. The solution to that is to use a good anti-fungal. Find one at your local plants store or use a sulphur or copper fungicide. The marks won't go away, but they will turn paler and will become less noticeable as the plant grows.

I have a couple of plants with this condition that I've successfully treated.

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I had the same pale yellow fungi in my pride of Barbados pot , but probably 5 X larger . I pulled the first 2 and threw them into the back yard ( wife did not like the look of them). The weather turned warm and I moved the pot outside, and it grew a couple more which I left. I just looked and there is one more about the size of photo in my pot. As a wild mushroom picker ,it never occurred to me to wear gloves. Very unlikely that the mushrooms have anything to do with the cactus. Supplemental : The mushroom looks like Lemon Yellow Lepiota , Lepiota lutea, poisonous. Common in compost, in greenhouses and house plants ( north America).

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  • I prefer to wear gloves when handling unidentified life forms :) – Roman Apr 9 at 6:04

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