Growth on upper mandible?

[Weaver]

A few guys have mentioned to me that they are seeing this 'growth on their birds upper mandible.
It doesn't wipe off and doesn't respond to mite treatments, Vaseline or the like.
Some well known finches suggest euthanasia but to me it looks more like a fungal infection.
Any ideas?
Bob.
Can't load the photo as it is too big apparently.
Further information' All birds are in mixed collections but only affects the painteds. Seems to not discriminate between young and old birds.
Cock birds seem more susceptible. Birds are otherwise healthy

[Craig52]

Painteds are renowned for scaley mite infections on the bill and it's a lot harder and takes longer to get rid of it. You will have to catch up the bird and place in a cabinet and apply moxi directly to the infected area twice a day as well as a couple of drops to the back of the neck or the bare patch under the wing which will give the bird access to the moxi whilst preening under the wing which won't hurt it to ingest. Craig