Oxalic Acid Vaporiser Treatment on September 20th

After the high count in Aqua from the drone trap last week – 50:100 and the Defra advisory on incidences of high Varroa infestations I decided to use my new vaporiser and apply Oxalic Acid to the home apiary colonies. Will do the Mole Valley ones next week.

Oxalic Acid Vaporiser - completed

Bit of a faff removing the entrance blocks especially as it was the middle of the day and as the weather has continued to be warm the bees were very active. Didn’t see the vapour coming out of the top of the hives but certainly seems effective based on the drop counts. Very easy to use and found the on/off switch to be useful, also liked the fact the battery is relatively light weight so easy to move around the apiary.

Put in Varroa slides before applying the treatment and the 24 hour drop counts were shocking:

  • Aqua – 132 – surprised at how high as this the colony that I have been very focused on drone trapping during the season
  • Blue – 212 mites, might be down to the poor start it got during the season
  • Cyan – 180 mites – very active so after the other results not too surprising
  • Denim – 37 mites, surprised how low it was compared to the others; hopefully the treatment was applied correctly This has been a very active colony throughout the season
  • Honeydew – over 300 mites. Very surprised as this was a new colony this year but I obviously haven’t been managing it for Varroa very effectively. I thought the it would be one of the lowest as it was set-up as a nuc and I didn’t use drone trapping.

Second count 48 hours after treatment not much better (either the treatment is really effective or my colonies are in a very bad state!):

  • Aqua – 85 mites
  • Blue -180
  • Cyan – 60
  • Denim – 10
  • Honeydew – 260

With such high counts I will treat again in 3 weeks. This is one of the advantages of using the Vaporiser is that the treatment can be repeated.

Making an Oxalic Acid Vaporiser – Part 1

Since reading about the effects of applying Oxalic Acid in a sublimate form (vaporised) rather than the trickle method I have been using I decided to look at acquiring a vaopriser. I was horrified to see what they cost for a commercial one and so set about making my own.

I couldn’t find a design that seemed to be tried and tested so experimented with various prototypes and have ended up with one that works for me – see under plans for the details of the build. This post is about my experiments and conclusions about what worked for me. I wanted to make it cheaply and if possible using tools that I have.

My initial design criteria:

1) Fit into a hive without removing entrance block

2) Use 12v power supply

3) Administer 2g dose within 3 minutes

4) Use my pillar drill and router to machine the materials.

Prototype 1:

I worked out the volume that 2g of Oxalic acid would take up and produced a Sketchup design for one that could be  heated by a diesel glow plug. Using my router I made the recess that would hold the Oxalic crystals to the correct dimensions . Then tapped 2 holes to take the glow plug and handle. Finished version of the block shown as 1 in photo. Found it very difficult to rout out the recess with a router bit in my pillar drill. Definitely not recommended and forced me to look at alternatives for the other versions I made. The drawback with this design is that it was relatively quite a large block of aluminium (50mm x 50mm x 19mm) and weighed 120g and took ages to heat up – over 5 minutes to boil off some water, so no good.

Prototype 2:

For this design, 2 in photo, I decided to try and use a PTC element to heat a slimline block. The idea being that using the PTC element would mean that I could keep the height of the unit to 9mm and so fit into the hive without removing the hive entrance block. Overall size was 60mm x 60mm x9mm and weighed around 60g. Because the tolererances for the various holes needed to be much tighter than I could achieve with my basic tools, I got a friend to CNC the block for me. The PTC element was cheap about £5.00 and could reach a temperature of 170°C, more than hot enough to vaporise the Oxalic Acid (157°C).  The drawback was that the PTC element heats up quite slowly. It couldn’t boil off the water I used as a test in less than 8 minutes, so I didn’t even bother to test with Oxalic.

Prototype 3:

Design 3 in photo. I set out to minimise the size of the block and went back to using a glow plug as the heat source. My friend CNC’d 2 for me so I had a spare if I messed up drilling the hole for the glow plug (he drilled and tapped the hole for handle). Overall the block is 42mm x 36mm x 12mm and weighs 45g

My first try was to use a 8mm aluminium tube for the handle as I wanted to pass the wires from the battery through the tube rather than have them taped to the side. This meant the wires had to be thin gauge to fit into the diameter of the tube. However on testing it showed the wires were not capable of carrying the current required to power the glow plug. Took about 3 minutes to boil the water off and the wires themselves were warm to the touch a sure sign they were not up to the job.

So my final version was to use a 10mm tube which could take wires rated at 13 amps (glow plug seems to draw about 5 amps).  I finished off the build with a wooden handle into which I  fitted a rocker switch. The acid test (forgive the pun) was that it managed to vaporise the Oxlic Acid in 2mins 15 seconds.

Oxalic Acid Vaporiser - completed

So my conclusions for anyone considering making their own vaporiser. Keep the size of the block as small as possible. I could probably shave about 10g off my version if I pare down the size a bit more. Use a glow plug as the heat source as it heats up really quickly and is cheap, around £5 for a new one. Beware the glow plug thread is fine  pitch, most taps seem to be for standard pitch.



Annual Oxalic Acid Treatment

Annual treatment with Oxalic Acid for Varroa control. Temperature around 9°C, bit warm but didn’t want to leave it any later in the month as one of the main triggers for the queen to lay is day length.

Didn’t open up the hives, just applied 5ml of Oxalic acid to each seam of bees.