I have never treated for Nosema... I am not sure fumagillin is as effective on the new strain of nosema.
O.K., so let’s say that you have found out which of your colonies (or yards) are actually infected, and that you’re uncomfortable with the spore count. You ask, What treatment(s) will actually work, and how best to apply them? At this time, the only well-documented successful treatment for N. ceranae is fumagillin, sold as Fumagilin-B®. If it is given to infected colonies at normal label rates in gallons of heavy syrup, it is generally effective against ceranae. But not as consistently as it was against N. apis. Also, be aware that since N. ceranae thrives during summer, it can fairly quickly rebound after treatmet
As far as OA the package can be treated under a cardboard box after removing the caged queen. I would use 1/2 dose or 1/2 gram.... no I have not done it because I have not had a package in years but that is what folks are recommending.