I have used OAV in top bar hives that had a hole drilled in the bottom that allows the wand to be pressed against the bottom of the hive.  Last year this time, 3 hives had counts in 18-20+ per 300 from an alcohol wash.  I did OAV multiple times over the winter.  The hives made it, and were strong enough. This year, never saw counts above 2/300.  ;)  looks like this worked.  I will treat in Nov and Dec.

OK, the OAV WILL COAT the comb directly above it.  Won't spread past 3-4 combs on either side of wand - so like bars 1-8 if your hole was at bar 4.  Keep those physics in mind when administering this, if you have a screened bottom board - if the cluster is long, you may need to adjust your protocol to get good coverage.  Also if you do not have a completely clear wand - no gray or black residue present - then you did not get a good burn.  I re-administer OAV in that case right away.  Wear gear that protects your mucous membranes - you know, eyes and lungs and stuff like that.  They will be damaged by OAV exposure.  

Sadly, in the US it is illegal to administer OAV when honey supers are on, which for a top bar means those honey combs present during the winter intended for spring harvest.  One option is to move aside the honey combs, temporarily put an airtight divider between the OAV zone and the honey combs, and remove after.... hmmm, I am not sure how long a divider between honey supers needs to be in place, for a traditional hive.  Anyone?  At least 10 min.  

Practically speaking, you ingest 1 g of OA when you eat 100 g of spinach.  You administer 2 g to an entire hive.  I don't worry about OA poisoning for honey for my personal consumption.  But the law is what it is.  

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