Hi Kevin,
First thanks for the podcast. Excellent source of information - and keeps me company when I'm out and about.
Reason for posting is that I've just read an article in The Beekeepers Quarterly - not sure if you know the publication as it's mainly European based - which I found interesting and would value your views on. It's by Ann and Maciej fron Opole in Poland and concerns their experience of using of Rhubarb to control varroa mites. Now I'm not sure if you have rhubarb in the US but that Yorkshire delicacy of rhubarb and custard (do you have custard is the US?- I'm sure you must) has a particular zing to it and that zing is caused by low levels of oxalic acid in the stalks.
Ann and Maciej have been experimenting by laying rhubarb leaves across the top bars in the brood box. The bee's work to clear the leaves away and in the process release low levels of oxalic acid throughout the bood box. They claim a natural mite fall rate increase of between 2 to 7 times during the summer months when it's particulalry hard to treat for varroa and leaves the hive in good shape for conventional autumn treatment in that varroa counts are at reasonably low levels when conventional autumn treatment starts.
They're still doing work on the topic and I'm sure more will come of it but it might offer a low cost (no-one has a use for rhubatb leaves), low tech (just open the hives and place the leaves in - the bees do the rest), natural (rhubarb is a foodstuff so no medicinal certification needed) route to varroa control.
Have you heard of this method before? Is it likely to be effective - and can you see any problems if the method is adopted?
Keep up the good work
John N.