A report out of New Zealand looks at a variety of "organic" methods including various thymol products and mesh floors

In autumn 2008, mite numbers increased rapidly. In those hives treated with organic control
products, there was still an increase in mite numbers over the treatment period. Initial
results indicate that treatment with organic products in mid to late autumn was not effective
at controlling varroa.

All the beekeepers found that mite numbers increased while the organic treatments were in
the hives. The number of mites in each hive doubled, and in some cases there were twelve
times more mites than before treatment. For example, before treatment there were 8 mites
in a sugar shake of 300 bees; after treatment with thymol crystals (24 days) there were 102
mites in a sugar shake.

Among the hives from all 6 beekeepers, a total of 18 out of 120 (15%) colonies died during
the autumn treatment period. Twelve hives from 3 of the beekeepers died because varroa
levels became too high, despite all hives having fewer than 40 mites per 300 bees before
they were treated with an organic product. The colonies that survived had all been treated a
second time with a synthetic product.

In autumn, because organic treatments did not effectively control varroa and the varroa
levels were very high after the treatment, we recommend that any hives with more than 40
varroa in a sugar shake after being treated, should then be treated with a synthetic control.

Because the number of mites increase rapidly during autumn, we suggest that beekeepers
who wish to use organic treatments, treat their hives early in the autumn to knock down
varroa numbers. At this stage it is extremely important that beekeepers monitor their hives
after treating with an organic product, as it is likely that the product will not be effective at
keeping varroa numbers sufficiently low. At least if hives are treated early enough in the
season and the organic treatments are found to be ineffective, the chance to treat hives with
a synthetic miticide and reduce the risk of losing hives to varroa is still possible.

2008–2009 Trial

The results from the 2007–2008 trial suggested that the organic treatments were not able to
effectively control varroa when applied to the colonies in autumn (March). Because of this,
we tried to assess whether a low level of mites before conducting the autumn organic
treatment had any effect on the efficacy of the product.

Discussion 2008–2009

Varroa control

The varroa levels from all of the treatment groups pre and post spring treatment and pre
autumn treatment were all less than 5 mites per 300 bees. Based on the thresholds of “20”
and “40 mites” that were used in this trial the data suggests that a spring Apiguard®
treatment controlled varroa as effectively as Bayvarol® over summer, providing the autumn
treatment was conducted before the first week of February. In the post autumn treatment
assessment the Apiguard® colonies had significantly more mites than the colonies treated
with Bayvarol® but of the colonies that were treated by the first week in February (n=90) only
14.4% required a second treatment and only an additional 7.7% (n=7) of colonies had more
than 40 mites and required a synthetic treatment. In comparison, 100% (n=15) of the
colonies that were treated after the middle of February had >100 mites per sugar shake.

Sustainable control of varroa
Taylor MA, Goodwin RM, McBrydie HM, Martinez OD, Evans LJ.
July 2009


[ this mirrors our experience in NYS. If the treatment could be conducted in early August (= February) it would be effective. This is why we were so keen on getting the mite away quick strips. Frequently by the end of August levels are already too high and treatment cannot be applied until the end of September, as our best honey flow is in that month ]

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