Hi,  I'm not working into band and fair organs but there is a similar
problems with reed pipes in many church organs.  The causes are not
popcorn but mostly flies, ladybugs looking for places to hibernate in
fall, and the occasional bees and other beetles.

It is worst if the organ is situated right under a south-oriented large
window.  Insects entering the church by any other windows or doors
would be compelled to fly towards the most lighted south windows and
will try to escape there.  After they are dead they accumulate on the
window sills and fall into the pipes of the organ below.  That's not
much of a problem if these are large flue pipes, but if they are reed
pipes these would stop speaking when clogged by the insect, or even if
a small piece of the beetle would lodge itself between the shallot and
the tongue.

In the 1920s and '30s the Casavant organ building company used to place
a screen on reed pipes at risk of being muted by insects.  That is the
only solution I've known for the problem in my 35 years career.  The
screens were a thin ring of wood, cardboard, or thin reed from which
baskets are made, onto which a piece of fine cheese cloth was glued when
it was applied to large 16' and 8' pipes in the lower octaves.  For
smaller reed pipes Casavant used a very fine cheese cloth or even
nainsook fabric glued directly on top of the resonators.

A major flaw of that solution would be that with time dust collected
in the cheese cloth, impairing the tuning and voicing of the pipes.
These would have their pitch going lower and lower with time, and
tuning them implies sending the tuning spring lower, too.  In doing so
the pipes will loose their voicing characteristics and start to sound
muffled or dull with slower speed to speak.

Such screens needed frequent dusting and raised maintenance cost so
Casavant abandoned the practice in the late 1940s.  Nowadays on organ
restoration projects when we encounter an organ that was previously
equipped with such screens these are systematically removed and discarded
by everyone in the business.

This insect and dust protection screen method can be applied to vertical
reeds that are not showing to the public but I don't think these
screens to be applicable to fair organs when the reed pipes are on
display.  And, if you think about using them, be prepared to delicately
clean the screens often enough with some vacuum cleaner set to the
minimum power available.

Another flaw: nainsook is fragile and it dries, becoming brittle, after
a few years and then has the tendency to fall apart inside the pipes.
These fragile screens might need replacement after about 10 to 20
years, more often if they are broken during the frequent vacuum
cleanings.

Gilles Chouinard - organbuilder
Laval, Quebec, Canada