Hi , I have seen it before on a nobile Dend. that came from Hawaii , it is from the sugary sap they produce . High humidity , warm temps. , I used diluted Physan on a cotton ball and removed it , this year none , be sure it is getting good air circulatiion , and not wet at night when the temp falls . The spores blow around and land on a prime area to grow the sugary sap on the plant . I called the place in Hawaii and they said they usually wipe it off before shipping guess they missed mine hope this helps a little . Gin