Good discussion all. All of my experience is in my own yards here in eastern WA. I have used a 3% dribble, 50ml per double deep in early winter as a broodless application for at least 5 years with no noticeable ill effect on the colonys at first spring inspection. This past year I experimented with OAV (vaporization) at 2g per double deep for both late summer/fall treatment and again early winter.
The late summer treatments took either 4 or 5 treatments at 5 day intervals to get mite counts down to my standard >1%. I did not see any ill effect on bees or brood but feel that the time and travel were a poor comparison with my standard 3 applications of 65% formic on mite wipes. I use 50ml on 2 Dryloc pads (25ml each) each time at 7 day intervals. At that concentration I get only very little brood kill and no queen loss and get mite counts down to said >1%. My winter loss has always been very low 15% max 5% normal with both methods. 

My question for those that have concern about oxalic is compared to what? Of the tools that we have I believe it is the most benign and yet effective as a winter application and a good fall treatment if you so choose and can figure a schedule that achieves the desired result. There will always be conflicting studies and data but local personal experience trumps all in my opinion. It is very difficult to pars out what was to blame on poor colony survival as Pete eloquently points out but there can be no argument with consistent success.

Paul Hosticka
Dayton WA

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