Good question Clyde. My thinking was this. As Oxalic Acid is only affective on hatched bees (not on Brood), then an early application when the hive is essentially bloodless will be the most effective, this is also supported by most of the reading that I have done. In reading around the net (I know, that is not always a reliable source of information), there has not been a resistance to OA treatment with many years/decades of use in Europe and other countries (yet). This would be more of a prophylactic treatment to help start off the bees season in a nearly mite free state. Last year it seamed to work well but I did not do a side by side comparison of early treatment and not as I only had 3 hives. Much of the reading that I have done does indicate a late fall or winter treatment is very effective and that summer OX treatment is less so due to presence of brood. so, One treatment now or a succession of treatments later in the summer when there is brood present, or using Apivar or one of the other chemicals which I do not like to use in my hives.
I was putting this question out there to hopefully start a discussion to get more information for myself and other back yard beekeepers so thanks for the reply and please keep it coming.
And, no, if there were still snow and cold weather in Bend I wouldn't be thinking of this but it has been warming up lately (very early) and the girls are flying and so I'm trying to get ahead of the season. I'm hoping my bees don't just burn through their available food supplies before spring actually arrives and nectar and pollen are around so I am starting to use sugar patties and some frames of honey saved from last year and the girls are going through it for sure.
Again, thanks for the reply.