BEE CULTURE: CATCH THE BUZZ February 5, 2015
By Alan Harman
There’s great news for beekeepers with the U.S. Department of Agriculture seeking approval for the in-hive use of oxalic acid dihydrate to control Varroa mites.
It’s a treatment long used in Europe that kills up to 97% of mites in a hive,
The government’s Federal Register lists an application for Environmental Protection Agency approval for the product, long successfully used in Europe in the colony against Varroa.
The notice is signed by Robert NcNally, director of the Biopesticides and Pollution Prevention Division of the Office of Pesticide Programs.
A spokeswoman at the EPA’s Office of Pesticide Programs confirmed receipt of the USDA application.
Approval of the application would give U.S. beekeepers a new weapon in their fight against Varroa.
European beekeepers say they successfully use vaporized oxalic acid, or a 3.2% solution of oxalic acid in sugar syrup, as a miticide against Varroa.
It can be used in both the liquid form and as crystals that can be evaporated by electric heater pans.
Oxalic acid had been successfully used by beekeepers in the United Kingdom for several decades to kill Varroa when Sussex University conducted a study to determine the effectiveness of different doses and application methods of oxalic acid on mite and bee mortality.
The experiment involved 110 hives comparing three application methods and three different doses that was completed in 2014. Hives were treated in early January 2013 when they had no brood.
Oxalic acid does not kill Varroa in sealed cells, but rather kills mites carried on the bodies of workers and also those crawling in cells not yet capped.
The researchers determined the proportion of mites killed by washing the mites off a sample of about 300 workers bees immediately before and after 10 days of treatment with oxalic acid.
They also determined the number of bees killed at the time of treatment, together with hive mortality and strength four months later in spring.
The university says the results came to a clear and encouraging conclusion. Application of oxalic acid via sublimation, where it is applied in its pure form by vaporizing the crystals with a special heated tool, was superior to application as a solution via either spraying or dribbling.
Sublimation gave a greater kill of Varroa at a lower oxalic acid level and showed no increase in bee mortality. In fact, four months after treatment, the hives treated via the sublimation had more brood than the 10 untreated colonies.
The sublimation method is quick and easy, as the hives do not need to be opened.
To confirm the results, the sublimation technique was retested a year later in broodless honey bee colonies.
“An amazing 97% of the Varroa were killed by using 2.25 grams of oxalic acid per hive, and colony survival three months later in spring was close to 100%,” the university says.
It says beekeepers only need to carry out this treatment once a year because it reduced the number of mites so dramatically it takes them a long time to build back up again.
The Federal Register notice says the application potentially affects those involved in crop and animal production, food manufacturing and pesticide production.
Comments must be received by the EPA on or before March 6.
Oxalic acid dihydrate is a colorless, odorless, crystalline solid. It is potentially fatal if swallowed or inhaled. It can also cause discoloration, irritation and burns of the skin as well as permanent damage to the eyes.
One operating manual says all employees who handle this material should be trained to handle it safely.
“Areas in which this compound is used should be wiped down periodically so that this substance is not allowed to accumulate,” it says.
In Canada, the British Columbia Ministry of Agriculture says oxalic acid dihydrate should only be applied in late fall when the colony has no brood. Any open brood in the colony is likely to be killed by oxalic acid.
“Even though the product is not as volatile as formic acid, always wear rubber gloves and safety glasses when handling the product,” it says “Avoid inhalation of vapors.”
The ministry says it should be applied only once.
“Oxalic acid can be applied at cool temperatures, either through vaporization (crystals heated and converted directly into a gas vapor) or trickling an acid-sugar syrup solution onto the bees.
One European expert goes even further.
“It cannot be stressed too strongly that oxalic acid is an aggressive substance and needs to be treated with respect,” he says. “Acid resistant gloves and goggles should be worn and an apron of the type used by mortuary attendants, along with wellington boots that have the tops covered by gaiters so that any falling liquid cannot fall into the boot.
“A respirator that has specialized organic acid filtering will be required in cases where the acid is sprayed or vaporized.”
The EPA is also seeking comment on an application from Certis USA L.L.C. to market a product called BmJ WG with a fungicide that claims to reduce plant viral infections and Bacillus mycoides isolate. It is intended for use on almonds, citrus, cole crops, cucurbits, fruiting vegetables, grapes, legumes, lettuce, pecans, pome fruits, potatoes, spinach, and sugar.
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