Helen,
I don't have a set plan. I see the infestation loading and decide on the best course of action for me/them at the time. Most times it is obvious and mostly nothing too precipitate/urgent. There is often a month to decide what to do, if it is not clear at the time, so no real worry.
IPM as per some of the DEFRA publication is a good grounding. I don't want to be making my new nucs from infested colonies, so am choosy where I get my bees from, or would give them a clean-up if deemed necessary. I might even oxalic some in the season if I thought it the best route. A good sugar rolling seems to get rid of most of the mites - but only good for broodless units. I prefer not to keep on drone culling, as a regular attack on the mite, but would ruthlessly remove all drone brood if it were badly affected. Culling the first capped brood is a good weapon after attacking the phoretic mites in a broodless colony
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I have removed capped brood to other colonies and then hammered the remaining mites, followed by later strengthening with flying bees, or treated bees; basically a shook swarm for the one colony and 'theft' of flying bees from the other colonies later - if I have moved one or other colony away to another site, it may affect my next attack on the mite.
I am just careful when swapping bees/brood around, as regards health of the bees. I have always moved bees to and from the OSR/beans/OSR (if available)/back to home apiary and have not generally suffered with excessive mite loadings in the 'foraging' season. Probably not as low as Finman and other commercial operators would want, but low enough for me. I did have problems early on (particularly saw the two colonies I bought, really struggling with the mite infestation) but have learned how to keep the mite down to safe levels - it used to be relatively easy, before mite resistance to pyrethroids.
If I had expanded further, I would have needed to be more regulated in my approach to the problem and treat all colonies more uniformly, but I am not; I intend to reduce my colony count, so with fewer colonies I can relatively easily keep ahead of the varroa - one way or another.
Look at it this simple way - A/S them all, and treat both halves when broodless, then re-unite. You lose some crop but not a lot. Phoretic mites are an easy target and you don't have to get rid of them all, just as many as you can, enough to get them through to the post-harvest thymol.
Post-harvest is the most important period for me. Clean bees brooding clean winter bees is my real target later in the year; healthy bees into winter as strong colonies is a priority to make wintering as easy as possible. There has to be a very good reason, now, to take a weakish colony into winter. I learned that from my second year, when my expansion plans went backwards!
I always like to have a contingency plan, should things go wrong. I don't use apistan strips as a regular treatment but would, should the weather turn too cold for thymol. Maybe not ideal, but good enough to get the bees through the winter or to an oxalic treatment - yes, oxalic would be used if felt necessary for the health of the colony!
So the underlying plan is to have as many options as possible available, and pick any (or every one) as the opportunity arises. Not using all stocks for honey production is another option - again, I have not been too worried how much honey I have got in the past - as long as it has been sufficient!
The most important thing is to recognise when treatment is likely necessary - no 'head in the sand' and just await the time for apiguard. Using any IPM opportunity which becomes available, at little cost to the bees/harvest will help them on their way.
Recognising the need for treatment is likely down to experience of knowing they are there and will be multiplying - doubling every month - and requiring careful checking to be confident they are not going to get out of control; suddenly finding a mite drop, when treated, of several thousand is definitely to be avoided! It will happen at some time, for all of us, that the mites are excessive. Part of my plan is that it will not be most of my colonies at the same time!
Hope this helps you think about all the alternatives available. Oxalic acid in the winter can reduce the need for a lot of these IPM alternatives, but will never cover all the possibilities; nor should it be assumed that the mite infestation is low, because sooner or later, you will get caught out. Even the great Finman admits to it!
Most get caught out for one of two reasons. First, they don't know what they are looking for, or secondly, they assume they are safe. Once the first is overcome, there is little excuse for getting caught out on a regular basis for the second reason. For those with only one or two colonies, extra care is needed if you don't want to risk having to start again.
Regards, RAB
Or even those misled by "no drop", like me.
