Dave Eyre writes that dysentry (Nosema) comes from poor stores.   I
assume by that he means from stores with too high a moisture content.   I
respectfully disagree.  Remember that bees must dilute their honey to about
50% moisture before thay can eat it, so even 15% moisture honey is diluted to
the "poor stores" catagory before it is used by the bees.   Also, at least in
Maryland we have been taught that high moisture in a hive is caused by poor
ventilation, not by feeding weak sugar syrup at an inopportune time.   As an
engineer, I can tell you that in a well ventilated hive, none of the normal
methods of feeding sugar syrup will noticably increase the relative humidity
in the hive.
     The danger from feeding weak syrup is that it may stimulate the queen to
lay eggs (as if it were a nectar flow) during the winter period when brood
rearing is not desired.   In fact, some of us will begin deliberately feeding
1/1 syrup in late February to stimulate brood rearing in preparation for the
start of our nectar flow in late April.
     As to when to feed the bees, I agree with David that Fall is preferred,
but in general any colony that has less than three frames of honey must be
fed promptly, regardless of the season.   Cold weather feeding can be tricky
because the bees may not be able to move to the feed, but it can be done (at
least in Maryland's climate).
 
W. G. Miller
Gaithersburg, MD