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> I wanted to ask folks who have used the oxalic acid
> dribble treatment for varroa during broodless
> periods in the fall/winter if you have seen any
> changes or a time shift in the spring brood rearing
> in their bees.
>
> I have read in the Swiss studies that the OA can
> show spring build-up problems but did not give any
> specifics.

This concern seems in the air. At the last Qc beekeepers annual meeting, I heard at least one important beekeeper reporting similar observation. Another one said he heard the same in BC for OA drizzling. We were then asking questions about OA mechanism of action on varroas and possible difference between drizzling and vaporizing methods.

> From what I understand, low pH of OA solution would be the main factor of varroacide action.

We are reassured from Finland.

Several European countries joined to study oxalic acid dribbling. If I remember right that was during years 1996 - 1999 or somewhere there. Same tests we done in different years in different countries.

First  result was that  the effect was much better in sugar/water solution than in water alone. After that the right dose was searched.

Some were too small with only 60 - 80 % effect, some were too much. Overdose makes the bees to be restless during winter and kills a lot of bees.  The optimum was found to be 75 g of acid / 1 litre of water / 1 kg of sugar. And the application 4 ml / Langstroth frame fully covered with bees.  With this dose there is as many bees in spring as in untreated controls.

In Finland we have not seen any delay in spring brood development. At the moment about 60 % of hives in the whole country  are treated with oxalic. Mainly by dribbling, less than 10 %  by vapour method.

Based on my experience the problems in spring brooding could come from overdose rather than the treatment itself.

Ari Seppälä
Finland

BEE-L has an excellent international group and we get the perspective from all over.  This one brought in comment form Quebec, Switzerland, and Finland.

I treated with oxalic in the fall (drizzling method), for the first time, using exactly the protocol described by Herve, in Maine, after queens had quit laying. We got great mite control, and build-up this spring is, if anything, better than I've been seeing for a few years. Relieved of their mite load they are charging ahead. Naturally I've been looking pretty hard for any signs of ill effects from a new treatment and I can't see any. So far.