Oxalic acid treatment
In districts where the bee colony density is low, such as in (Dalsland, Sweden), no varroa treatment before the autumn is needed. In fact, only one fumigation with oxalic acid steam is required during the broodless time. In any case, the amount of naturally fallen mites on bottom boards should be followed and be recorded.
In Finland, the normal concept of varroa treatment includes oxalic acid trickling when the colony is broodless or contains very little brood. This usually takes place in November or December and in the early spring right after the cleansing flight. This is done by trickling 4ml 3.2% oxalic acid per fully occupied beeway on adult bees.