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Oxalic Acid Demonstration


  • It should be assumed that Varroa destructor is now present in every hive, and all beekeepers must make preparations to establish an integrated pest management system to control it.
  • Throughout the year there are various methods of organic and chemical control.  The last chemical treatment of the year is usually applied in late summer or early autumn. 
  • However, there is a long interval of time (possibly 6 months) between this last treatment and the first hive openings of the spring. 
  • During this time, the Varroa mites are able to continue breeding and multiplying their numbers as long as there is brood in the hive.  
  • For this reason, it is recommended that, for those hives with open mesh floors, pull-out inspection trays are used to monitor mite drop throughout December and January.
  • The tray is put in on day 1, left in for approx 7 days, removed, mite numbers counted and the number of mites is divided by the no. of days to give a daily mite drop figure.
  • If during this time, the no. of mites exceeds 1 per day, treatment with Oxalic Acid should be considered.
  • Oxalic acid only kills mites that are out on the bees (at the Phoretic stage) – not those in brood cells. 
  • During the bee brood rearing season, approx 85% of Varroa mites are in sealed brood cells at any time (only 15% of mites are on adult bees) so treating when the colony is as broodless as possible (end Dec – mid Jan) gives maximum chance of killing mites.
  • CAUTION !!!  Oxalic acid causes lasting damage to the broodnest: it kills brood and the queen will not lay in those cells for a long time after the dead brood has been removed.
  •  This treatment must ONLY be done when broodless (end of Dec/start of Jan). 
  • The following makes enough for 40 hives (it only keeps for a few weeks, so try to get together in a group to avoid waste – DO NOT KEEP MIXES FOR NEXT YEAR !!!
  •  1kg Sugar, 1Litre water, 75g Oxalic Acid Dihydrate.
  •  Make up syrup & dissolve crystals.  Fill 50ml syringe.
  •  Apply 5ml solution along every seam of clustering bees. 
  • (It is a good idea to practice on an empty broodbox with a syringe of water – 5ml is a very small amount - only a teaspoon !  It must be evenly distributed along the seams of bees).
  •  If your bees cover a brood & a half, do both boxes.  Work quickly to minimise heat loss.
  • Can be bought ready made from Thornes (Approx £2.75 for 2 hive treatment). 
  • Oxalic Acid Crystals to make your own: 500g: approx £8.38 (enough for 250+ hives).
  • After Oxalic Acid treatment, check the pull out tray for 2 weeks to monitor numbers of dead mites.
  •  Oxalic acid treatment should only be used to supplement Thymol treatment – the main treatment should be Apiguard.
  •  Varroa is a vector for viruses – it will KILL a colony if not controlled.