Oxalic Acid is a naturally occurring acid found in plants. It became popular in Europe & Canada for treating Varroa Mites in a honey bee hive. The most effective time to treat a hive with Oxalic Acid is when a hive has little to no sealed brood. It cannot penetrate capped brood so it will have no effect on the next generation of mites that were left in capped brood. If there is capped brood, it is advised to treat once a week for three to four weeks to treat all iterations of emerging brood. Best beekeeping practices in Colorado is to treat both spring and fall when there is little capped brood; however, if you have an infestation, you can treat any time during season. Make sure any honey for human consumption is removed before treatment.
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 vapor. Smoke bees up from the bottom board. Place 1g Oxalic Acid Dihydrate powder (per deep hive body) into vaporizer. Follow the vaporizer manufacturer’s directions for use. Insert the vaporizer apparatus through the bottom entrance and seal with damp rags. Apply heat until all Oxalic Acid has sublimated.
Note: To completely dissolve Oxalic Acid Dihydrate, use warm syrup.
Dissolve 35g of Oxalic Acid Dihydrate in 1 liter of 1:1 sugar water (weight : volume). 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 does is 50ml per colony whether bees are in NUCs, single, or multiple brood chambers.
Under certain unfavorable conditions (e.g. weak colonies, unfavorable overwintering conditions), this application method may cause some bee mortality or overwintering bee loss.
DO NOT let Oxalic Acid make contact with skin, eyes, or be ingested. Wear proper personal protective equipment (rubber gloves, safety goggles, long sleeve shirt) when mixing or distributing Oxalic Acid. If exposure to skin or eyes does occur consult directions and safety sheet for instructions. If severe reaction occurs, call 911. Wash hands, exposed skin, and PPE directly after treatment to avoid contamination.
You will want to treat your hive TWICE: once during early spring and once during the fall/winter after all honey has been harvested for human consumption. Honey bees that have a lot of capped brood will need multiple treatments. (Treatments should be one week apart for three weeks to get all emerged brood).
Dried, unmixed Oxalic Acid should be kept in a cool dry place and will not expire.
Mixed solution can last up to a week at room temperature and a few months if kept in the fridge.
IF THE SOLUTION STARTS TO TURN TAN/BROWN OR SMELL FUNNY DISCARD IMMEDIATELY. DISCOLORATION MEANS AN ALTERNATE CHEMICAL [HYDROXYMETHYLFURFURAL] IS FORMING AND IS TOXIC TO BEES. DISCOLORATION CAN BE CAUSED BY LONG EXPOSURE TO THE SUN.