I (and many members of my orchid society) regularly use flowers of sulphur on orchids (notably on areas that have been cut or broken); pyrethrins should also be OK. Basically, where you might use cinnamon, you can use sulphur.
Generally, you want to avoid buds and flowers no matter what you're spraying with - if they're infested with something, I'd generally rather chop them off and save the plant.
There are several products in the Natria range
Natria | Bayer Advanced
I assume you're talking about
NATRIA Insect, Disease & Mite Control | Bayer Advanced
?
I would say it *should* be safe, but orchids are a fairly varied group, from things that faint and die at the merest suggestion of less than perfect care to the sort of thing that can be tossed out with the trash and continue to grow...
So you might like to test it on one or two "volunteer" plants before you spray everything. Remember plants do things slowly (most orchids particularly so), so it may take some time (weeks even) to show ill effects.
I'm generally pretty gung-ho with treatments - if a thing is sick, it's getting treated with whatever I have to hand that is most suitable; I'll google it for orchid doses if they exist, otherwise, I'll follow what is on the packet/label, judging by whatever is closest (e.g. ornamental plants or flowers etc).
---------- Post added at 12:08 PM ---------- Previous post was at 12:06 PM ----------
A very traditional mixture (read about it in ancient gardening books) for fungi was something called "bordeaux mixture" which I vaguely recall being sulphur and copper sulphate. It's not very widely used any more, presumably as things have become resistant to it.
---------- Post added at 12:09 PM ---------- Previous post was at 12:08 PM ----------
Oh no, my bad, bordeaux is slaked lime and copper sulphate.
Bordeaux mixture - Wikipedia, the free encyclopedia
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