Oxalic acid 99.6% is for the control of Varroa mites in honey bee colonies. Apply in late fall to early spring when monitoring indicates treatment is necessary. Do not use when brood is present.

Administer Methods

Solution
To completely dissolve oxalic acid dihydrate, use warm syrup. Dissolve 35 g of oxalic acid dihydrate in 1 litre of syrup made from a 1:1 sugar: water (weight: volume) mixture of sugar and water. Smoke bees down from the top bars. With a syringe or an applicator, trickle 5 mL of this solution directly onto the bees in each occupied bee space in each brood box. The maximum dose is 50 ml per colony whether bees are in nucs, single, or multiple brood chambers. Under certain unfavourable conditions, e.g., weak colonies, unfavourable overwintering conditions, this application method may cause some bee mortality or overwintering bee loss.
140 grams Oxalic Acid is needed for 4 liters sugar syrup and will treat 80 hives. Especially for this applications Medivet developed a drench gun, the Optimiser™.

Vapourizer
Apply only to outdoor colonies with a restricted lower hive entrance. Seal all upper hive entrances and cracks with tape to avoid escape of oxalic acid vapour. When possible, treat while hives are wrapped to ensure they are properly sealed. Smoke bees up from the bottom board. Place 2.0 g oxalic acid dihydrate powder into vapourizer. Follow the vapourizer manufacturer’s directions for use. Insert the vapourizer apparatus through the bottom entrance. Apply heat until all oxalic acid dihydrate has sublimated.

Dripping
Dissolve 185 g Oxalic Acid Dihydrate in 4 litre of 1:1 sugar syrup or 6 ½ oz in 1 US Gallon
Pour 5 ml of this solution between each occupied bee-space onto bees.

Trickle (recommended in Ontario)
Prepare 50% sugar syrup (eg. 1 kg of sugar in 1 litre of water). Measure 1 litre of syrup and add 35g oxalic acid dihydrate (min. 99.6% purity) crystals. Agitate the solution by stirring vigorously or shaking. The crystals dissolve best if the sugar solution is warm (not hot). All the crystals must be dissolved. Prepare the solution within days of treating the colonies and keep refrigerated until use. 1 litre of the oxalic acid solution will treat 20 colonies.

Oxalic Acid Directions (.pdf)

Instructions:  https://pr-rp.hc-sc.gc.ca/1_1/view_label?p_ukid=273530598