Oxalic acid is a very effective treatment against Varroa mites when used appropriately.
Api-Bioxal is approved by the FDA for use in honeybee hives - most other forms of oxalic acid would be considered "off label" use and incompatible with best practices.
We recommend using a Heilyeser vaporizer and providing oxalic acid treatments when the hive is broodless (October, and mid-winter in the northeast) or when outdoor temperatures are inappropriate for other treatments. When using OA vapor during active brood-rearing it is best to give the hive five treatments, five days apart.
Use at a rate of 1 gram per deep hive body. Available in a 35 gram bag or 350g