...the legend exists at last!
Dyckias from a more dry region are all under fungi attack in humid climates.
This dark spots are fungi and may be controlled by a more aerated position
and the use a domestic anti-fungi derived from pine resin.
To eliminate the fungi one may rely on very dangerous and unsafe products.
Systemic drugs are all very dangerous.
I kept the plants ventilated and I use a much less toxic anti-fungi substance.
This problem occurs specially during Winter and its humid, less windy and dark days.
Fungi need humidity to feel fine and the fact Dyckias do not know how to live in less Sunny and more humid spot they do not know how to fight back the fungi.
They just do not have this problem in nature.
Joinville is one very humid place with air relative humidity always touching 100%.
Some years ago it was said to be impossible to keep Dyckias in Joinville.