Bill wrote:

>>This quantity corresponds to 5 – 6 ml for each occupied bee-space of a Dadant or Swiss hive.

I tried to apply 5 ml per each bee-space and experienced affected queens last spring.  But understand from Ari from Finland, that it should be 4 ml per bee-space in a Langstrogh hive and the dose must be in proportion to the amount of bees.

>>*Time of treatment: *In broodless colonies (November – December)

I applied the OA on Dec. 13, 04.  It was a balmy day and the application took only a few minutes per hive.

>>· only *one *treatment in autumn

I've also heard that it should one treatment per queen.  In other words, subjecting a queen to more than 1 treatment, can affect her laying.  Some advocate re-queening annually for this reason.

>>· perform the treatment at an ambient temperature above 0o C

A Swiss website suggested temps > 5 C.

>>...use one pint of water, one pint of sugar, and 1.168 ounces of
Oxalic acid (same as about 2 1/3 tablespoons, or 7 teaspoons, or 2
tablespoons plus 1 teaspoon- all level and be precise)

I used a gram-weight scale to get an accurate concentration.  The recommended rate results in a somewhat strong solution - I some solution left over after the treatment and it eroded the shiny coating in the metal coffee can after several days.

>>Application: ...drip 5ml of the mixture from end to end between
frames for each hive body (or frame of bees).

It should be emphasized that the solution amount should be directly proportional to the number of bees covering the frame.  The full dose should applied to a bee space fully covered by bees.  If 60% of the space is covered with bees, apply only 60% of the dose.  (I had not made good approximation of the bee coverage and applied the full dose, I think, that's why had queen problems in the spring build-up.)  When in doubt err on the lighter side.  You will still kill a lot of varroa.

I think OA is just about the best treatment for varroa today.  I've seen a single varroa since the treatment.  In a study, OA treated colonies showed equal or lower OA concentration in honey - OA naturally occurs in honey - compared to control colonies.  There is no wax contamination.  But one must develop a good feel for the OA application amounts and apply to broodless colonies which means catching those few warm days in the late fall or early winter in the North.

The control is very cost effective.  I bought a small container of OA at a local hardware store for ~$5 and with my number of colonies, it will last ~10 years.

Waldemar
Long Island, NY

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