Help! yellow - orange plaques in my cactus

[qiyao]

Hi everybody,
I have 2 barrel cactus and both have some yellowish - orange plaques.

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The short spined one seems less afected:

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In the base of the cactus seems shrinked

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The long-spined one I bought it recently (1 week ago) and it suddenly becomes yellow without doing nothing. I planned to leave it 2 weeks before repotting to let him adapt to the new house. When I bought it, it was green without any noticeable problem.

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Also only one side of the cactus is affected, not the entire cactus. This is the side that do not receive sunlight.

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Other data:
- I live in south Spain (Mediterranean climate, this month minimum temp is 7-8ºC (45F moreless).
- Both plants are located in south oriented balcony, so light is ok.
- Only watered once this month. The one that I bought 1 week ago did not water yet.

What could the issue be? I think that the new one I bought carried some type of fungus since the store and also infected the old one I have...

[anttisepp]

First reminds mites second sunburn. Maybe both burned it happened easily ones in the open air.

[qiyao]

I have been researching and the second one is 100% sunburn. The plant was for a month inside the store without receiving direct light, I give it too much sun too suddenly.

The first one I am still doubting between mites or rust fungus

[ohugal]

Photo's 5 & 6 remind of symptoms my E. grusonii had several years ago. They developed when I suddenly put it in full sun. I'm not saying it's identical. Your's has it on the side and not so much on the top of the plant.

[anttisepp]

E grusonii is very tender to sunburn till it established.

[qiyao]

Hi,
Can someone give some advices for the short-spined cactus? The spots didn't stop although using systemic fungicide + peroxide mix. It slowed down a bit, instead of big spots now appears a lot of small spots around the cactus.

[MikeInOz]

Hi,
Can someone give some advices for the short-spined cactus? The spots didn't stop although using systemic fungicide + peroxide mix. It slowed down a bit, instead of big spots now appears a lot of small spots around the cactus.

The pot is a bit big so maybe it stayed too wet during some period in the summer? Systemic fungicides will not work on cacti more than 1 cm in diameter IMO. You can try to puncture the areas directly with a needle and inject some full strength fungicide like chlorothalonil or your systemic. This has worked many times for me with succulent orchid tissue. It will not heal but it stops the spreading. If it is bacterial, fungicides will not help of course. Also, grusonii does not like very cold temperature. It may not be a primary infection but tissue damage from cold/wet/UV. This damage becomes the seat of infection in the future. It is often just guesswork with cacti problems. Does it get plenty of calcium and potassium?

[qiyao]

The pot is a bit big so maybe it stayed too wet during some period in the summer? Systemic fungicides will not work on cacti more than 1 cm in diameter IMO. You can try to puncture the areas directly with a needle and inject some full strength fungicide like chlorothalonil or your systemic. This has worked many times for me with succulent orchid tissue. It will not heal but it stops the spreading. If it is bacterial, fungicides will not help of course. Also, grusonii does not like very cold temperature. It may not be a primary infection but tissue damage from cold/wet/UV. This damage becomes the seat of infection in the future. It is often just guesswork with cacti problems. Does it get plenty of calcium and potassium?

During summer here it is incredibly hot and also the soil is pretty gritty so I think is more a winter related issue. I have noticed that 2 days after a rain it usually worsens a lot a lot, so probably is something fungal or humidity related. I discard humidity because I have a good drainage soil and the grusonii receive plenty of sunlight.

As to calcium and potassium I am not sure, I added a tiny bit of fertiliser in the last repotting (october). At least potassium levels should be ok, I will try to add some calcium. Additionally, I will try the puncture method with a new fungicide.