Re: Visible mite drop after 3rd round of Oxalic Acid vapor - go for 4th round?
I don't want to discourage anyone from doing a 4th or greater OAV treatment if the colony needs it, I usually just do 3 but I did 4 this year too. The weather allowed for extended brood rearing and the mite populations climbed pretty high in Aug-Sept.
Originally Posted by Matt_inSC
I believe the 3 treatments, 7 days apart schedule covers a 21 day brood cycle period based on the "capped brood" after the initial 1st treatment. All of the capped brood at the time of the first treatment will have emerged 14 days later, and on the 3rd treatment all bees will have been exposed to OAV. I know there is not 100% efficacy, and the residual effect of the crystals may not last the entire 7 days until the next treatment, but under normal circumstances "most" of the mites will have been impacted after the 3rd treatment.
There are always some mites that escape the OA and end up under capped cells, so you can't get them all. But after the 3rd treatment one should expect to see the fall drop off rapidly with each successive additional treatment.
To everything there is a season....