mix 100g sugar + 100 g water + 7,5 g oxalic acid.
This enough for 3 two box hives or 5 one box hives.
Cost is almost nothing.
This recipe is linked to from this post
from 2011, to which I can't reply, so I'll reply here. I think it's important when mentioning the oxalic acid recipe out of context that it is a recipe for dribbling and not for spraying.
I'm only a 2nd year beekeeper so my knowledge on oxalic acid is theoretical. Please correct my information if you think it is incorrect. But this is what we learnt in beekeeping class:
Oxalic acid can be applied in two ways: dribbling and spraying.
Dribbling works best on a winter cluster, from above, because the bees are clustered and will spread the acid among themselves with very little wastage. Spraying can be done in summer, and must be done directly onto the bees, so one must either spray each frame individually (time consuming), or spray the bees all together after shaking them off into a bucket (e.g. when making splits). It is said that a new colony made from bees sprayed in a bucket will be practically varroa-free.
Oxalic acid can't be vapourised, because after the water has evaporated, the crystals remain on the wick, when they should be on the bees.
Oxalic acid can't penetrate closed brood, and since most varroa is in the brood, oxalic acid will therefore be ineffective in removing most varroa if there is closed brood.
It is unclear how oxalic acid works, but it is thought that it kills varroa in two ways: directly by contact with the acid, and indirectly by drinking the blood of bees that drank the acid syrup. Since queens don't drink sugar syrup, it is considered safe for the queen to be present during treatment. Oxalic acid may kill some weaker bees and some open brood.
Always wear gloves and safety glasses when using oxalic acid, and take plenty of rinse water and a mobile phone with you. Do not underestimate this acid. If you get acid on your skin or in your eyes, it won't burn immediately but you'll notice the injury after a few days.Dribbling:
100 ml water + 100 g sugar + 6 g acid crystals = 3 colonies.
Works best if outside temperature is just below or above freezing.
Make the solution lukewarm so that you don't freeze the bees.
Dribble directly onto the bees in the winter cluster, from the top.Spraying:
300 ml water + 8 g acid crystals = 3 colonies.
Works best if no closed brood is present.
Ideally suited for making broodless splits or creating packages.
* Method 1: take out every frame and spray the bees.
* Method 2: make room between frames for nozzle, and spray down into hive.
* Method 3: shake bees into a bucket, and spray them in the bucket.
Example method for spraying when making a split: put the queen, 3-6 broodless frames of bees, and foundation and/or feed into a new hive, and spray it in its new location. New queens emerge in the old hive on day 13. Spray the old hive on day 27. Check if the new queen survived on day 33.