[Laurieston]

Does anyone have any experienc with Oxalic Acid for the winter treatment of hives against varroa ? Recommendations? Concerns? etc..

I am being recommended it by fellow beekeepers but don't know much about it.

Any thoughts would be appreciated.

Laurieston

[anderso]

if you have  never used this treatment, I would  ask one of your follow beekeepers (or your local Association) to show you, as it can damage the colony  if done  wrong,
 
There is plenty of info about this but seeing been done is best.

[ZacB]

if you have  never used this treatment, I would  ask one of your follow beekeepers (or your local Association) to show you,

Second this. We use as part of our treatment against Varroa. A Thymol treatment late spring and then Oxalic Acid trickled over the bees around this time of year. Same as a lot of things - easy when you get the hang of it. Drawn up in to a syringe and then 5ml trickled over each full seam of bees. Need to be careful on when applied as it will kill any brood I do believe, so usual to apply approx three weeks after a good cold spell.
There is also a method of vapourising Oxalic crystals but have never used or even seen this way of applying. A little info / insight into what is used.
http://www.thorne.co.uk/health-and-feeding/varroa/oxalic-based?product_id=1712

[Bionic]

These are the Dec 2012 details from out local bee keeping club.
The winter bees now occupying the hive should live for many months if they are
healthy.  Long enough to maintain the size of the cluster over the coldest
months and keep it warm, produce brood food to feed developing larvae early in
the year, and start foraging operations in the spring. Work in the apiary since
taking the honey off has been concentrated on achieving a hive full of healthy
winter bees. So varroa control in August/September, feeding in September/October
and also frame changing earlier in the season should have ensured fewer
pathogens and more cell space filled with stored honey/syrup and pollen.  If the
winter bees are infected with viruses or nosema, their lives will be shortened
and they cannot produce so much brood food. In this case colony numbers will
dwindle and the infection will be passed on to the developing larvae, which may
not survive: this is one way a colony dies out over winter.
You cannot wind the clock back to feed with syrup or change frames now, but you
can treat for varroa with oxalic acid and keep Deformed Wing Virus at bay. We’ve
just had a reasonably cold spell, which will ensure that queens have stopped
laying and that colonies will be entering a broodless period. We’re at a time
where one can assume there is minimal brood in the hives and treatment with
oxalic acid is feasible, without inflicting damage to any sizeable amount of
brood, or having it harbour most of the mites present in the hive. I am of the
opinion to treat soon, rather than wait for a colder spell, before brood rearing
begins again next year. I would also urge to treat sparingly, according to the
size of the cluster and not to overdose.
When applying oxalic acid or hefting the hive to check for stores, it’s a good
time to make sure that the entrance is clear of dead bees, or any other
obstruction, with a twig and even a torch: don’t worry if you pull out a few
dead bees, that’s normal. It’s also a good time to double check that mice cannot
get into the hive and the roofs won’t blow off. If you want to relocate any
hives a short distance, it can be done now, while the bees are not flying.
Oxalic acid is applied as 3.2% oxalic acid in 1:1 sugar solution using a 50ml
plastic syringe with a wide bore needle. It has an efficacy of about 90% and
will mop up mites that escaped the Apiguard treatment. It will also kill mites
that have bred since then and those that have come into the hive from external
sources.  I recommend that you buy the solution ready made. It is available from
all beekeeping equipment suppliers at reasonable cost and avoids the risks
associated with preparing the solution from crystals. Oxalic acid solution is
poisonous and should be used and stored safely. It should be very pale in colour
with no crystals formed. If the solution is darker than straw colour or has
crystals, don’t use it. It should not be stored for the following winter as
there may be a build up of HMF that is toxic to bees.
Oxalic acid only kills mites that are living on the bees, in the phoretic stage.
It does not kill mites in the brood. When there is brood in the hive, only about
15% of the mites are found on the bees and the majority (85%) found in the
brood. It follows that oxalic acid works best on colonies that are broodless at
the time of treatment. This is most likely to be the case in December to early
January. Removing the floor insert to ensure good ventilation will encourage the
bees to have a broodless period. It is worth noting that oxalic acid will kill
open brood, so it can be used on both natural and artificial swarms that offer a
broodless period.
Treatment is best carried out in cold and dry weather when the bees will be well
clustered. I would use either thin gloves or none at all, certainly not thick
cumbersome ones. Wear a veil and have a lit smoker handy to smoke them down when
you’ve finished, as you risk squashing them when replacing the crown board. Fill
a 50ml syringe with oxalic acid solution (ideally at blood temperature) and
trickle 3 – 5ml of solution between the frames along each seam of clustered
bees. Only treat once and do not overdose, a small colony may only require half
the syringe or less. After the oxalic acid treatment has been completed the
floor insert should be cleaned and put in place to monitor mite drop. Mites will
continue to fall for about 2 weeks after which the insert can be removed.