>>The problem with OA from the research I have done is keeping the 
hive below varroa threshold until the broodless period.

This is true.  I use this to my advantage to select breeder hives 
that can handle varroa loads from one fall to the next w/o any 
additional treatments to raise queens from the following spring.

>>The second problem is figuring the exact kill you got is hard as 
many times it takes a couple weeks for varroa to die.\

I don't bother counting mites since I am sure of the method's 
efficacy (to my surprise, I don't see varroa in capped drone comb 
until the following September or so).  I place 1" thick styrofoam, as 
winter insulation, under the screened bottoms in the late fall before 
the OA treatment.  When I remove the styrofoam in the spring, I do 
see a lot of mites in the debris.

>>Many beekeepers are going to OA alone. I believe you need to treat 
at least once with another treatment in our area. Apilife var and 
apiguard have been the most used treatments in our area.

Another late-summer treatment may be needed in areas where very large 
bee populations are required to make it through very severe winters.  
In my area (zone 7, downstate NY), just the OA dribble seems to work 
fine.  In some hives I will see PMS bees in October but the colonies 
don't collapse and winter fine.  We do get several good days here in 
the winter for cleansing flights.

Waldemar

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