Some Gymnocalycium covered with salts coating?

[Snowcat]

Hello everyone!

I have a question about some Gymnocalyciums. Some flat slow growing gymnos, like G. spegazzini, G. ragonesei, G. occultum are covering with something that LOOKS like a coating from slats that are left after water drying. I am not sure this is really a salts lefover, but it surealy looks like it.

Look what I am talking about. This plant is more then 10 years old...


This is a 3 years old seedling, G. speggozini


This is another 3 years old seedling, G. occultus


This coating appears ONLY on some gymnos. All my plants sit in the same soil, recieve the same watering.

Other gymnos do not have it, look at this one for example.


Other cacti also don't have it. Look at Thelocactus bicolor


Or this seedling (not sure what is it), it's 2 years old and recieves ecactly the same care as spegozzini seedlings.


Only flat, slow growing Gymnos appear to bo covered with something that resebles salts lefover fomr water drying. BUT even if I take my water and let it drt several times on something, the leftover will not be THAT visible. It looks like these gymnos are filtering water through themselves and release salt on their skin. Is that really so?

P.S. My substrate has NO Calsium in it, just quartz and perlite.

[iann]

It might be from the cactus itself. Many cacti develop waxy or powdery coatings. Sometimes you don't even notice, but if the coating is disturbed then it looks a bit like this. Copiapoas and Pilosocereus are some better known examples, but the dark Gymnocalyciums do it too.

[K.W.]

Good morning Snowcat,

looks bad. . . sorry.

Wax ???
How are the thorns secrete wax?

Looks to me like a fungus. Or even lice. . .

Close up picture available?


Best wishes

K.W.

[Snowcat]

Hmmm fungus that eats ONLY one genus and only slow growing brown skinned plants? Is that even possible? It does not spreads to others, it is not something new in my collection, so I am sure it's not contagious.

Maybe it's dead already now... I've gave my plant anti fungus treatment in Spring, so maybe it's not contagious just because it's dead already and I see just the consequences....

I can take an extreme macro shot tomorrow (more then 1:1), I'll post the picture...

[Snowcat]

Ok I could not sleep and decided to take pictures now,

Here are 2:1 shots. Twice closer then "true 1:1 macro", so very fine details are visible. Still look as salts for me...

[jfabiao]

It looks a lot like red spider mite damage. Here's a picture of a 2-3cm Lophophora that got attacked pretty badly last spring:

710461612-RSM.jpg (78.08 KiB) Viewed 2554 times

The little buggers have minds of their own and choose certain plants. Rebutia, Chamaecereus/Chamaelobivia and Lophophora are especially appreciated. You will be able to see them with a 10x loupe if you look carefully.

[Snowcat]

It looks a lot like red spider mite damage

Yes, this looks really alike. But you can clearly see the mites on your picture... And I don't see mites on my cacti, not with a loupe, not on photos. Maybe they've "visited" my collection at summer (when I was absent) and then they left somehow... Anyway, I'll spring something anti-mite on my collection to be sure.

[SoilSifter]

I thought it might be pest damage, too. Pests often have a preference for certain plants in a collection. However, your close-up photos are very close and I can't see the pests. I doubt that is mineral excretion. There's stuff on the spines.

[cortez753]

Taste it, many cacti secrete a sugary substance out of their areoles. How do you know it's salt?

[Snowcat]

Taste it, many cacti secrete a sugary substance out of their areoles. How do you know it's salt?

This was not a joke, right?
Because I did it No, it's not sugar. It tastes slightly bitter.

[cortez753]

Lol! No, it's no joke. I have no idea what it can be then. Maybe your theory is true. "It looks like these gymnos are filtering water through themselves and release salt on their skin."

[Steve Johnson]

Good to see you active on the forum again, Snowcat!

My guess is that the slightly bitter taste indicates the presence of salt buildup on the skin. But why on some cacti and not others? Could be that some species have stomata which are large enough to pass salts through to the skin in transpiration. If you're watering with tap water, this will cause bicarbonate buildup in the pot over time. If you're watering only with rainwater, salt buildup can also come from fertilizer. Assuming that my stomata theory is correct, then the salt coating you see on some of your cacti is the obvious sign of a salt problem that is impacting all of your plants. More info on your watering/fertilizer regimen may be helpful.

[K.W.]

Dear cactus friends,
dear snowcat,

fungal infection or mites!
Thorns have no stomata. As the salt get there?
And. . . Salt does not taste bitter, it tastes salty.
And looking at the edges of pots. The pots of diseased plants also have the infestation.

10372752_m.jpg (116.86 KiB) Viewed 2473 times

I would paint with methylated spirits. Careful!
If the coating dissolves, no salt.
Also, I would dig up the plants.
I bet 100 to 1, there are lice to the roots.

Best wishes and good luck!

K.W.

[7george]

Salt (carbonate) can be tested with vinegar, the solution should produce small bubbles. If you don't sprinkle your cacti with hard, salty water quite often you can not have such a layer of salt over them. The build-up from watering stay around the soil surface level on the stem or pots.