Sick Pleiospilos nelii

[LuzNegra]

Hi everybody!

I have some questions regarding a couple of Pleiospilos nelii plants that have been attacked by a disease or pest. Hope anyone can help. Sorry for the long message.

One of my Pleiospilos nelii v. rubra plants started to become soft and brown, and rotting at the base. As this happened a couple of weeks after receiving it, I first thought this was due to damage during transport, but 3 months later, more Pleiospilos plants in the same pot started to rot. Upon inspection, I saw little white-grey bugs, the size of a springtail, on the compost and under the pot. I decided to treat it with horticultural soap and quarantine it. As it seemed it was too late to save it, I decided to throw it away in the end. Unfortunately, I took no pictures of the plant or pest.
A couple of days later, my other Pleiospilos nelii plant (from another seller), in another pot nearby, started to become soft also at the base, so I treated it with horticultural soap and neem oil, together with the plants that were nearby. I also quarantined it. The rotting (or "softening") seemed to stop, but the spot were the plant started to become soft has somehow dried, and it now looks deformed and has what seems like a "scar" (pictures below).
Today one of the stems of my Avonia papyracea, which is from the same seller as the rubra plant, also collapsed, so I'm worried the disease is spreading.
Any idea what could have happened? Was this due to a pest, or did the pest just attack a plant that was already sick? The plants did not have any sticky residue, nor bugs on the leaves themselves. I don't think they were overwatered, as I only water them every 10-14 days, with a day temperature above 30°C.

Here is an image of the rubra plants taken by the seller, before I got them, and images of the damage done to the other Pleiospilos plant.

pleios.jpg (38.51 KiB) Viewed 1807 times

Thanks for reading and sorry again for the long post!

[iann]

Sounds like fairly classic rot from overwatering, soggy soil, or too little sun, possibly all three. Even in Spain! The pests sound like they actually are springtails, which would confirm too much water. The photos do look strange though. Pleiospilos can rot to a soggy mush or to a harder dry husk, I suppose depending on the pathogen that takes over.

The soil should be allowed to dry between watering, completely, as in don't water if the soil is still damp. Also watering should be limited during hot weather (what we in England would call very hot weather), possibly stopped completely. P. nelii grows best during cooler weather, or at least cooler nights. It can be watered lightly in hot summer conditions in England but I don't know how far that can be pushed. The plants should get some direct sun, enough to colour them slightly bronze rather than very very green. At the very least a good dark green. Lastly, your soil looks very dark and is probably better-suited to regular houseplants than to very xeric succulents. More coarse material, probably something less absorbent like grit, but possibly something like bark would work in your climate.

Same for the Avonias, probably. Double for the gritty soil, they don't have huge roots and the tubers don't like sitting in soggy soil for very long. Lots of sun. Although some are from winter rainfall areas, they all seem to grow strongly in summer here.

[LuzNegra]

Hi Iann,

Many thanks for the advice!
I'm really relieved to know that this could just be a cultural problem.
I never thought I could be overwatering them. I'm more used to succulents with woody stems, which are less prone to stem rot, I guess. The soil of the rubra and the avonia is the same they came in, so I don't really know what it is. I potted the green Pleiospilos in standard commercial cactus potting mix, with a topping of pumice, but repotted it in plain cactus potting mix when it showed signs of damage. Maybe this potting mix, which usually goes well with my other succulents, holds too much water for these more tender or "fleshy" plants. I will repot it in a mix of mainly pumice or coarse sand with just a little bit soil, and limit watering during these warmer months.
I will also repot the avonia, just in case, as it seems that the original potting soil is problematic in my conditions.
The only thing that still seems strange to me, is that the rotting stopped as soon as I used the horticultural soap. But this could be just coincidence.
Here is another picture of the Pleiospilos. The color is not as pale as it came through in the first post.

Best regards,

[iann]

I see better in the new photo. It does look like it is rotting as the base of the leaves. Although these and the Avonias are both leaf-succulents, they need far less water than many others like Crassulas or Echeverias. Because they take less water, they don't dry out the soil as fast, so it is best to use a soil that doesn't hold too much water all at once.

The colour looks a bit better on that P. nelii. Should be getting enough sun in Spain. It is hard to give them too much, but it is possible to scorch them if they don't get good ventilation. They're very adaptable, can grow in summer in cool climates, but possibly in winter for you. I've had flowers in July and in December, so take your pick.

Avonias are much harder to cook no matter how much sun you give them.

[LuzNegra]

Today I repotted the Avonia in a soil mix of mostly pumice. Hope this helps, so that the rot does not spread. When I removed the old soil I noticed that it was indeed too water retentive. It had not been watered in about a week, but nevertheless the soil was quite moist, even with the plant growing in full sunlight. It seemed that the soil was almost completely organic, there was no perlite, sand, or anything similar in it. From now on I will be more attentive to the soil the plants are delivered in, that's for sure.
Thanks again for your help!