Re: Does oxalic acid leave long term residues in the hive?
The problem I see with the single trickle method in the Northern US and Canada is that the recommendation is to apply only one treatment in the broodless period, late in the season. By then the damage has already been done, many times it's too late if the mites loads are very high. The treatment may have terrific efficacy at that point, but bees stressed by heavy mite infestation are already in decline and will struggle to make it through winter.
I like the two pronged approach. In late summer when the mite levels are skyrocketing treat with OA Vapor, 3 treatments one week apart. This will knock down a fairly high percentage of phoretic mites and allow for a healthier colony moving into late Fall/early Winter. Then when they are broodless treat with a single trickle of OA to clean them up.
To everything there is a season....