Late Autumn Varroa Treatment Without Risk of Residues

Factors to be considered when using the “Trickle Oxalic Acid Treatment”

The final treatment of the colonies in autumn or early winter is a component of many anti-Varroa

treatment regimes as for example the system in BadenWuerrtemberg. This treatment has the

aim of reducing the Varroa infestation level in colonies to an absolute minimum, so that in the

following season there is no problem with Varroa before the late summer treatment. In August.

This procedure has proved Itself to be effective in beekeeping practice.

The final treatment is carried out after the colony has ceased to rear brood. In this brood free

condition one treatment is sufficient to achieve an effectiveness of over 90%.Wh ire treatment is

carried out on colonies-which still have brood present the effectiveness is much lower.

The only methods of anti Varroa treatment which do not cause residues in the hive products are

with the organic acids such as formic and oxalic acids.

Of course the use of these alternative substances is extremely limited due to the legal situation

within the EU. An EU decree (1804/1999) regarding ecological animal husbandry allows the use

of formic acid, lactic acid, oxalic acid and thymol for the treatment of Varroa, however the various

Nation State regulations carry more weight. In Germany up to the present time there exists general

permission for the use of formic acid at a concentration of only 60%. This is unsatisfactory. In other

States more flexibility is permitted. In Austria the use of oxalic acid is permitted as it is in many other

EU States and also in Switzerland. When are Bee Colonies Free of Brood? Many strong colonies

with older queens cease to rear brood in October. In nucleus colonies with young queens this is

seldom the case. This might possibly be due to their development phase only ending in late summer,

while, the older stronger colonies have already reached their peak of development by June.

Brood rearing in autumn Is influenced by apiary location, but more so by the weather. The first night frosts

cause the queen to stop egg laying. Three weeks later the colony is brood free. At this time the oxalic acid

trickle method may be carried out. The removal of the hive roof and crown board to facilitate the treatment

has no detrimental effect on the bees.

Prior to Treatment- Check the Natural Mite Fall

Not every colony requires to be treated in the late autumn. A prior check on the natural mite fall carried out in

November is worth while. To facilitate this, an insert is placed on the floorboard. The natural mite fall check is

Carried out a week or two later. If the fallen mites are light coloured there is still Infected emerging brood in

the colony! If the natural mite fall is more than 1 mite/day a further treatment is recommended, more than 5 mites/day

needs immediate treatment. If untreated colonies indicate an average of 1 mite/day in November, this indicates

that there are still some hundreds of mites in the colony.

The overwintering capability of such a colony is not endangered, however by the following summer the colony

could be very heavily infested. Therefore treatment is recommended. If this is not done then in early summer as

a consequence drone brood sacrificial combs must be utilised.

Description of the Trickle Method

The treatment is carried out using either an aqueous solution or sugar syrup solution at an oxalic acid concentration

of 3.5% applied using a syringe or some other suitable device.

The procedure should be carried out in such a manner that it can be administered ‘drop by drop’. Oxalic acid may be

purchased in the local family chemist, It will also be available as raw oxalic acid. The acid comes as oxalic acid dehydrate

and consists of 71% acid and 29% water. The solution Is bottled In a secure capped vessel on which It Is possible to

write, ordinary tap water may be used to make up the solution. Any calcium in the water will combine with the oxalic acid

and precipitates as insoluble calcium oxalate crystals. The effect on concentration of the solution will be negligible.

The addition of sugar to the solution will merely result in a more rapid mite fall, It has no effect on the efficiency or bee

tolerance and also does no harm.

It is also possible to purchase ‘custom made’ solutions such as ‘Bienen Wohl’. During the treatment the weather must

be cold, a few degrees above freezing Is ideal. Smoke should be used only sparingly If at all If the colonies are clustered

tightly due to low temperature.

The colonies cluster under a deep crown of stores in November/ December. The treatment of colonies on single brood

chambers Is relatively easy since the cluster position can be seen. In the case of double brood chambers it is often more

difficult, especially if the bees are clustered in the lower box. The use of a torch may expose the position of the cluster

or the top box may be tipped up. In this way the treatment can be trickled into and not onto the cluster. It is best to take

a little care and time when treating. It is better to do two passes over each frame space. The more bees which are in

contact with the solution the better the treatment will be tolerated and the solution will be more readily distributed around

the colony.

According to the size of the colony the dose varies between 30 - 50 mIs. 30 mIs if the colony is tightly clustered in temperatures

under or at 0°C and only covering 4-5 frames, 50 mIs when the cluster is on 6-7 frames. The treatment must only be administered once. Repeated applications even with ‘Bienenwohl’ are not tolerated well by the bees. Large numbers of bees will become over acidified and fly prematurely and not show as mortality on the hive insert. In colonies free of brood a second treatment would be superfluous anyway.

The mite fall resulting from the late treatment should be noted and compared with the result of the initial findings for natural mite tall. The mite drop continues to increase over a 4-5 week period, even when most of the poisoned mites (80%) drop during the first week after treatment

THE TRICKLE METHOD

AT A GLANCE

Required:

1 - Aqueous 3.5% solution of oxalic acid or sugar syrup 3.5% solution of oxalic acid (200g sugar, 35g oxalic acid

dehydrate dissolved In ¾ litre of water), then more water added to solution to make 1 litre quantity or ^MBienen Wohl.

2 - 100 ml syringe.

3 - Acid proof gloves (important!).

How is treatment carried out?

Each colony is dosed with 30-50 ml of solution at dose of 5-6 ml per Occupied frame space.

When is the treatment carried out?

4 - Treatment In November or December at just above 0°C. Administer treatment in as many droplets of solution as

possible and drip onto as many bees as possible. (Do not shake solution onto bees!)

5 - Mite fall continues for 4-5 weeks.

6 - Good efficiency only in brood free colonies.

7 - Two applications is one too many.