Canadian beekeepers officially have a new tool to kill varroa mites now that the Pest Management Regulatory Agency has registered oxalic acid for use in Canada.
“We are just waiting for the PMRA to send us the final letter, but as far as we know, it is registered and the PCP (Pest Control Product) number has been assigned,” said Canadian Honey Council chief executive officer Heather Clay.
The PMRA gave ministerial permission to use oxalic acid in 2005, but it is not the same as an official registration.
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“For international trade it is important to have all chemicals used in the hive registered with the PMRA,” Clay wrote in a Canadian Honey Council newsletter in May.
The official designation is welcome news for honey producers such as Terry Greidanus, who farms near Cayley, Alta.
“It’s a tool to control varroa mites and we’re very glad that it has been registered here (in Canada),” said Greidanus, who is president of the Alberta Beekeepers Association.
“It’s another tool … and we need all the tools we can get.”
Oxalic acid is a natural substance found in rhubarb leaves, but the kind used on mites is a synthetic and highly concentrated product that kills mites through direct contact because of its low pH levels.
It is distributed through a beehive by either spraying or dribbling an oxalic solution or by using a process called sublimation, in which the acid changes from a gas to a solid.
“It gasses off into the hive and then it sublimates back to a solid, (distributing) small particles all over the hive,” said Murray Lewis, a beekeeper from Austin, Man., who started experimenting with oxalic acid this fall. “Then the bees rub on it and it gets on the mites.”
Mark Knox, a beekeeper from Nipawin, Sask., said oxalic acid is not the final answer, but it helps prevent miticide resistance, which can develop if beekeepers use the same chemical all the time.
“I use it. There’s probably eight to 10 beekeepers in Saskatchewan that use it.”
Oxalic acid is also finicky to use, said Rheal Lafreniere, an apiculturist with Manitoba Agriculture.
Beekeepers cannot use it when eggs, larvae and pupae are in the hive because the acid can kill the brood.
“It’s often used at the beginning of the season or end of the season,” Lafreniere said.
“So, it’s more of a cleanup. If you’re still concerned that you might have too many varroa mites left over after your previous treatment, you could follow up with oxalic acid…. It’s more of a secondary control product.”
Greidanus said the product should also be applied at cool temperatures to work properly.
“The temperature has to be right…. The cluster can’t be super tight. It has to be a loose cluster for the vapour to penetrate properly.”
Lewis said he’s excited about oxalic acid because it’s less harsh than other chemicals used to control mites.
“It’s more management intensive, but I think we’re past the days of putting in a strip (of miticide).”
