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Winter varroa treatment Oxalic Acid Drip

Posted: December 14th, 2018, 9:17 am
by slightmadness
Trying to figure out the best temperature to apply an Oxalic acid drip. I'm on the Eastern end of Long Island and it gets cold but we still have days well above freezing. I've been advised to apply an Oxalic Drip to control for varroa from a local beekeeper here.

From a basic online search it looks like the best temperature to apply is 35-38 degree Fahrenheit. I'm nervous about applying it when the temperature approaches freezing because I've only read about moisture causing mortality for bees. Dripping water based oxalic acid solution onto the cluster seems counterintuitive. At the same time, if I wait for a warm winter day my bees typically aren't clustered and are busy cleaning the hive and I'm concerned I'm missing lots of bees. Any thoughts on an ideal temperature to treat with an oxalic acid drip?

Thanks in advance!

Re: Winter varroa treatment Oxalic Acid Drip

Posted: December 14th, 2018, 10:08 am
by Allen Dick
A lot has been written about this, but finding it is always a problem, and, of course a lot of people offer opinions whether they know what they are talking about or not. In fact those who know the least are often the most certain.

I will write generally since I do not know the legality of such treatments in every locality and am providing information that applies here, where the treatment is legal.

At any rate, this is a treatment, so we first have to ask, why are we doing it? Treatments almost always have side-effects and some collateral damage, so the benefit has to be expected to exceed the harm.

Without knowing the history of a hive, any previous treatments, or whether it has been sampled for varroa, or whether varroa was seen on a drop sheet -- or the need is assumed since nothing has been done in the past year, I'll just deal with the question generally rather than give advice and specify a temperature, There are obviously times when it is too cold, but this treatment is used in summer temperatures with good success, so there is no upper limit AFAIK.

Let's analyse the process.

First, the intent is to apply the syrup to the bees, not to have them eat it, since it is harmful if ingested, so it is important the bees are not hungry or they will consume the drizzle and be harmed.

Also, the cluster must be loose enough that the syrup will penetrate the cluster and reach most of the bees +/- and not just run off the outside of a tight cluster.

The actual temperature outside is not critical. What is observed inside the hive and anticipated weather changes and time of day will determine whether to proceed or not.

A bit of smoke applied judiciously in advance will ensure the bees fill their stomachs, assuming adequate liquid feed is available in the cluster.

The oxalic acid product available is dihydrate. The industrial grade is as acceptable and widely available.

Mixing the dose correctly is important. People sometimes get confused by instructions that confuse oxalic anyhydrate with the dihydrate, and mix the wrong concentration, so use clear instructions from a credible source, not some random YouTube video.

The syrup should be freshly made and at body temperature. The amount applied should be no more or less than the recommended dose.

So, in short, pick a nice day when the bees are loosely clustered, smoke them and let them settle down, and make sure they have at least few hours before sunset to recover.

The rule in beekeeping is to plan, then observe and respond to what you see, not arrive with assumptions and carry on regardless, so let the bees advise you when you open the hive.

Re: Winter varroa treatment Oxalic Acid Drip

Posted: December 14th, 2018, 10:29 am
by slightmadness
Thank you for this very thoughtful reply!

Re: Winter varroa treatment Oxalic Acid Drip

Posted: December 14th, 2018, 10:47 am
by Allen Dick
You are welcome.

FWIW, here is an article I wrote some time ago. ... c_drip.htm