I'm hearing questions about oxalic.  I'm going to be publishing an article
on its use in ABJ this winter, and have started compiling notes.  I thought
I'd put them out to you all for your information, and comments.  IMO, we're
still early on the learning curve with oxalic, despite considerable European
research.

Oxalic acid syrup notes (© Randy Oliver 2006):
Oxalic acid is a natural component of honey and vegetables.  It apparently
acts as a contact poison to mites, and is about 70 times as toxic to mites
as it is to bees.  It needs to be mixed in sugar syrup to be effective, and
is transferred fairly well throughout the colony by the bees.
Oxalic acid dihydrate (not dehydrate) can be purchased in any paint
department as "wood bleach."  Check the ingredients label, or call the
manufacturer to make sure there are no added ingredients.  (Oxalic acid
dihyrate is  71.4% pure oxalic acid.)  It can be purchased cheaply in bulk
(less than $1/lb) from chemical supply houses.  

Oxalic application:
Oxalic is best applied as a dribble, not a spray.  To apply with a garden
sprayer (we especially like the Gilmour funnel-top "BackSaver" 1-gal model)
, pump up a medium pressure, then back off the nozzle adjustment until you
get a solid, weak stream that shoots out several inches, and doesn't splash
when it hits the bees.  Use a graduated cylinder or measuring cup to
calibrate how many ml your sprayer puts out per second.  Then figure how
many total seconds of "trigger on"  you need to apply the dose.  I adjust
the pressure and nozzle so that the right dose per frame is applied in 1
second, then I squirt for 1 second down each "seam" of bees between the
frames.  When dribbling, the best results will likely be from squirting the
dose directly on each seam, with the wand in line with the frames.  It helps
me aim to let the dribble squirt out at a low angle about 3-4 inches before
it hits the bees  (you can drag the tip between the frames, but you get more
splashing that way). Syrup that lands on the frame tops does not count--the
bees don't touch it!  Don't worry if your aim is off at first, it will
improve with a little practice. Research indicates that it's not critical to
apply the syrup evenly--the bees will move it around (but it's probably
better to apply it to evenly).  Total dose per colony is the most important
thing. 
We usually work in pairs, first working ahead to break  the brood boxes
apart, then returning for one person to tip the upper brood chambers back
and the other working the sprayer.  Ideally, we'd squirt each box of bees,
but this year we're only squirting the box with the most bees., adjusting
the dose per seam  to reflect the total population (e.g., squirt 1 sec/frame
if you're treating both boxes; 2 sec/frame if you're only dribbling half the
bees).  It's easy to treat a colony per minute, and not hard to move twice
that fast!  One large beekeeper reports that he gets better results
squirting both boxes of bees.  We find that two of us can treat 500 colonies
before lunch, dribbling tops only of busting colonies with bees across the
top, and splitting colonies not showing bees below the lid.
The bees normally do not react defensively to being dribbled with syrup. 
What you will notice, though, is that if the bees are heavily mite infested,
and look dull and listless, within a week after an oxalic dribble they will
look bright and peppy.  I know that "peppy" is not a scientific term, but
you'll see what I mean.
Mites will start falling dead in about a day, then heavy fall on day 2 and
3, then tapering off to about day 7.
Oxalic acid is well researched for a December broodless application.  
Accurately measure 3ml of solution per seam of bees, and treat only one
time, or you can harm your colonies.  E.g., for a colony with 10 frames
covered with bees, dribble a total of 30 ml of solution.  Mite kill is 90%
or greater!
Summertime application is more forgiving.  Use about 5ml per seam. 
Measurement is far less critical;  you can apply far more (or stronger
solution), and repeat treatments weekly 3 times  without apparent harm.  I
qualify this statement, since some European research indicates a lingering
effect of oxalic killing brood to some extent.  We haven't observed this to
be significant, but are watching (see
www.stratford-upon-avon.freeserve.co.uk/Newsletters/April2006.htm).  Mite
kill with 3 treatments a week apart is 60% or better.  We need more research
in this area (we're currently observing a group that we treated at 5-day
intervals)!
Tip:  you're stuck if your sprayer malfunctions--take more than one to outyards.

Mixing the oxalic syrup:
See the safety tips below.  Mix in a sink where you can rinse everything off.
Oxalic crystals do not measure well by volume, so you must have a scale
accurate to 1 gram to measure it.
For amounts less than a gallon, weigh the crystals., then pour them into a
quart or gallon jar with a plastic lid. Add half the warm water, and shake
'til oxalic is completely dissolved,  then add sugar, and the rest of the
water.  Shake until all the sugar is dissolved before putting the solution
into a sprayer--undissolved crystals will clog the sprayer!  It's tempting
to mix everything in the sprayer, but you'd be inviting problems.
The solution forms bee-toxic HMF in warm weather, so use within a week, or
refrigerate for prolonged storage.  Discard the solution if it starts to
turn brown.  It's cheap, so make plenty, then dispose of any excess down the
drain, or neutralize with baking soda.

Common Sense Safety:
Don't forget that oxalic acid is a poison!!!  The MSDS states:  "Harmful if
swallowed, inhaled or absorbed through skin. Corrosive - causes burns. Very
destructive of mucous membranes. May cause congenital malformation in the
foetus... Avoid contact with metals."  The LD50 is about 375mg/kg, which
means that if you were to drink 3 cups of 3.5% solution, it could kill you!
 Fortunately, oxalic does not vaporize unless you heat it quite hot (oxalic
vaporizers are dangerous since you can inhale fumes and kill
yourself--vaporized oxalic is three times as deadly as formic acid).
Handle the crystals very carefully, with chemical gloves and glasses. 
Luckily, oxalic crystals are damp and don't float in the air.  Wash your
hands and all surfaces before you rub your eyes or pick your nose!
Mix and store oxalic acid solutions in glass or plastic containers, not
metal (most common plastics are resistant to dilute acids). Clearly label
any container of solution.  Minimally state: "Poison  3.5% oxalic acid"
Once the solution is mixed, it's much safer to handle (for what it's worth,
the 3.5% solution is only about twice the oxalic acid concentration
naturally occurring in chives, parsley, and rhubarb!).  But be especially
careful not to splash it into your eyes, or breathe any sprayer mist. 
Dribble it at arm's length, and keep your face away.  If it gets on your
skin, wash it off with water.  Tip:  if you question whether any acid is
still on your skin after rinsing, just touch your tongue to your skin.  If
it tastes tart (like lemonade), there's still acid remaining (kids, I'm not
telling you to drink the stuff!).
Make sure you always have jugs of water handy to wash off spills--especially
in outyards.  Baking soda in the water will neutralize any acid.  Don't use
oxalic unless you have plenty of wash water at hand!
Make sure you use low pressure with the sprayer, so solution doesn't splash
or mist.
When using a garden sprayer, make sure you release the tank pressure between
yards (or applications), so no one gets sprayed in the eyes by bumping the
trigger accidentally!
      
Formulas:  (The following formulas are for w:w solutions of the dihyrate.)
To make approx. 1½ cups 3.5% oxalic acid solution (enough for 5-10
treatments), first completely dissolve 16.5 grams oxalic acid crystals in 1
cup warm water, then add 1 cup granulated sugar, and mix 'til clear.
To make approx. 3¼ cups 3.5% oxalic acid solution (enough for 10-20
treatments), first completely dissolve 33 g oxalic acid crystals in 2 cups
warm water, then add 2 cups granulated sugar.
To make approx 1 gallon (treats 50-100 colonies) of 3.5% oxalic acid w:w
solution:  dissolve 165 g oxalic acid in 5 pints warm water, add 5 pounds
sugar.  
Or mix one 12-oz tub with 1 gal + 1 qt warm water and add 10 lbs sugar
(makes about 2 gallons; treats 80 strong summer doubles, 40 strong summer
singles, or 145 8-frame mid-winter colonies).
Commercial beekeepers:  you can dissolve the oxalic in a little warm water
and top off with syrup.

© Randy Oliver 2006

-- Visit www.honeybeeworld.com/bee-l for rules, FAQ and  other info ---