Andrew Johnston wrote:

>QUESTION ONE. Will oxalic kill brood in any stage?
>QUESTION TWO. How late, ambient temperature wise, could oxalic be used

Question one is easy. As far as I know there is no problems to brood of oxalic drizzling treatments. And I have not heard complaints from evaporation either. The affects to brood is common misunderstanding, because every adviser stresses that the bees should not have brood. The reason for the advice is efficacy. If there is capped brood in the hive, and the total area is as big as mans hand, the efficacy is reduced to around 70 % from 95 % in broodless hives. Mites really concentrate to the last brood.

Average beekeepers don’t bother to check every hive about the brood. Therefore I have decided to advice to treat as late as possible. The colder it is, the less is the efficacy, but because of the affect from the brood it is safer to wait until snow stays in ground. Or to check every hive for brood before treatment. I have read some papers about the temperature/ efficacy and have got the view that when temperatures are around 0 C and below the efficacy is about 5 % less than when temperature is above + 5 C. So the difference is small compared to the affect from the brood.

The bees keep brood quite long in the fall. Just read a study that showed that in Southern England  there is brood almost all the year around.

Where would the line for average colonies with brood all the year around  be in North America ?

Availability of pollen and nectar affects a lot so there is big variation. Here in Finland we have seen almost 2 month differences in the end of brood period in average hives.

Ari Seppälä

Central Finland  62 N  24,5 E

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