I have heard Randy Oliver speak several times about his sponge method for oxalic acid application and have been attracted by the simplicity and relative safety as against sublimation. I have also wondered about the efficacy of trickling eg. how much trickles out of the open mesh floors. I also had a number of years when 40% of my colonies suffered with CBPV generally considered to be exacerbated by Varroa. I did not lose any colonies but they were certainly not of the strength of the non-affected hives. My Varroa control routine was a mix of Apiguard and OA trickling with concerns about Varroa's resistance to Apiguard being raised more recently.
For the last two years I have cut 5cm square Spongetex (Wettex in old parlance) and soaked them in Apibioxal which is an approved product. I did not make my own OA solution as, like it or not is not approved in the UK. The squares were applied damp, not dripping wet. Once the honey supers have been removed I place five of these on the top of the brood frames and then start my autumn feeding. When the feeding is finished, the feeder is removed and the sponges are left in place. I believe that Randy Oliver considers that the bees walk past the sponges and phoretic Varroa come in contact with the OA. The sponges are left in all winter when the mites are phoretic rather than in the cells of larvae, bearing in mind that even if in the current climate of warmer winters some colonies do not necessarily have a brood stop. Even when I feed fondant is given and then everything is removed by the middle of March when brood rearing really kicks off in style. One thing to note is that on removal the sponges are not dried out - still damp and sticky. The other plus is that OA is a poison and Varroa are not likely to become resistant. The sponges are washed, dried and saved for the following year and there was no sign of them being chewed by the bees.
Now I can't verify that this method is making a difference in Varroa numbers as I have not done any drop counts but what I can say is that I have had no oubreak in any of my hives of CBPV in the apiary since the sponges were used and the colonies have been strong and productive. It is early days I am not pushing the method, just saying that I am pleased that my bees seem healthier and I have not had the distressing sight of piles of dead bees outside the hives.
