White substance on cuttings

[HP22B]

I'm rooting this Trichocereus bridgesii cutting and lately have been noticing this white powdery substance on it and some of the columnars nearby. Anybody know what it is and what I can do about it?

Thanks!

[hegar]

To me this looks like some kind of exudate. Did you by any chance spray your plant?
I would just go ahead and wipe these white splotches off and see, if they do appear again.

Harald