Hi, nice to meet you!

Hi, Ct! Good to meet you, too!
I am a bit confused by the question, though. Do you mean an insecticide or fungicide dust? If so, what kind of flower, with what kind of problem? Or do you mean something else?

Hi Ct and welcome to GoY, like Tugb. I'd like more info before trying to answer your question. Answer could be as simple as pollen but more info needed first.

If its a yellow powder on the petals its almost certainly pollen

Not all pollen in yellow Stera.

I can't remember seeing another colour! What have I missed?

Orange on a dandelion for a start...

White on other plants and bright red/orange on some Crocus

Ive seen bright orange come to think. of it......and yes,my pale pink Christmas cactus has almost white. Must learn to think before writing!

Scilla siberica has blue pollen. I don't know if we are helping, though, Ct. You can answer our questions by writing in a comment, just as if you were answering your own question. Then maybe we can say something a little more sensible. Maybe more of the back story would help.

Wow!