http://www.beespace.me/rhubarb-bees-and-varroa
Through my University connections I managed to source the original paper that I had a Polish chap translate for me ( Our local DPD driver from a Beefarming family in Poland!)
I have been using the method.... hardly a comprehensive test but our MSc student carried out a dozen or so stickie board Varroa sampling on untreated Italian bees ( in BHS Polly Nationals) to ascertain a normal drop. One colony had a drop of 20+ compared to 2 and < 5 over 24 hrs. This colony had had a rhubarb leaf that must have blown off of the compost heap and found chewed up on the qx.
I have also heard tell that a 3% Oxallic Acid solution made up in VIMTO has a similar knock down on Varroa as the now banned Hiveclean had.
(3g OA made up to I00 ml with the concentrated fruit drink.)
VMD Licenced OA products are available to beekeepers in the UK
Yeghes da