jen,
this is a spring treatment method for treating with fumagilin. i am not familiar with the drench and/or spray. but have read some on both methods.
seems a lot less work to feed the bees a syrup pail or jar with fumagillin mixed in. also, i would be unable to drench my bees with this mixture, it would be too cold in my climate, both for fall and spring months. the other observation. this beek is mixing the fumagillin in and it is in clumps, at about 2:10, not sure how effective this would be.
EDIT AND ADD:
i found it best to dissolve the fumagillin in warm water first before i add it to a syrup mixture, so there are no clumps or particles......i have posted the directions for mixing up fumagillin before, will find it, post back.