So recently I’ve been playing my flute quite often (~2-3 hours a day) as I’m starting up a band again. Although I leave my case around 2cm open and swab the flute out well, the cedar plug in my Burns folk flute keeps growing hairy green and grey mold on the outside (The side covered by an endcap on most other flutes). Oddly, the inside seems clean. I cleaned and oiled it recently, and I keep it in a room with fairly steady 55% humidity. Any idea what’s happening?
Once you’ve had a crop of ‘green’, there will always be residual spores present. Two things will help. One a little more benign than the other.
Absolute alcohol ( not really the best thing on finishes and wood) will literally disrupt the cell walls of the conidiospores left in the cork. If you use this (actually the 91 % alcohol available in diabetic supplies at the pharmacy will work as well) just swish it about and then get it off the wood. A little more benign will be using a peroxide solution. Diluting the standard pharmacy 3% peroxide ten to one will effectively inhibit any spores from germinating and will probable not bleach or injure the cork or the wood. The humidities that are good for our flutes are also ideal
for the germination of fungi imperfecti spores. Let’s not bring up mites. . . 
Bob
You are probably keeping it too humid - easy to do here when we’ve had this blob of warm water in the North Pacific making it really muggy here all summer and fall. There is no need to humidify flutes here in Seattle, unless we get one of those rare winter cold snaps with heavy snows followed by a week or two of high weather and winds blowing the really dry air over the Cascades.
Contact me by PM and send me your address - I’ll send another cedar plug, ready to go. Or it might be best for me to look at the flute and make sure there aren’t other issues (and I will use 190 proof Everclear to kill any mold or algae growth in the bore).
Casey
Thanks, Casey, I’ll PM you.
The reason I posted is because rubbing alcohol (99% isopropyl) didn’t seem to kill it! In fact, I think it rather enjoyed the nosh!