At this time of year the most effective chemical is Oxalic acid. Apiguard (Thymol based) is less effective because of the low temperatures. Oxalic acid can be used in several ways although the only “legal” application method is by using ApiBioxal which has recently been given official approval (see BBKA News November 2015 pages 389-390).
Some beekeepers have started using vapourisation (sublimation) which involves heating the Oxalic Acid under the hive to give a vapour which spreads through the hive and kills the varroa. Although it still does not kill any varroa in capped brood it is claimed that it does not harm the bees and repeated treatments can be applied 5 days apart.
Sussex University has recently produced a Broadcast News Item on research they have been doing on the best way of using Oxalic Acid. They suggest that the vapourisation method is the best way. I attach a link to their Broadcast which makes interesting reading: http://www.sussex.ac.uk/broadcast/read/33537
If anyone wants to comment on how they have managed with the various different methods of treatment, please let me know. This might be helpful to members particularly as the first time using a different method can be quite daunting.
Sally Leslie, Tel: 01305 823043 email: firstname.lastname@example.org