Hi Michael and All:
 
>I've requeened lots of chalky colonies.
>Sometimes it works, but not very often.
 
That is my experience as well.  I think that if you wait until the situation
is quite severe that the break in brood rearing is not matched by the worker
population which is also decreasing.  I think it may be better just to unite
the colony with a better one.  I have also begun to think that broodcombs
with a lot of chalkbrood (especially with the black spore laden mummies) are
best destroyed or taken back to the rib and disinfected if they are plastic.
 
This year I went from 200 to 400 colonies.  I had the least chalkbrood I
have had in years due to a combination of putting honey combs in new brood
supers and one of the warmest springs I can recall.  The combination of
rapid spring buildup and cold nights seems to trigger it.
 
But I agree that breeding hygienic bees is the answer.
 
Regards, Stan