Now that resistance to Bayvarol and Apistan is widespread, it is clear that we will
have to use other means to control Varroa. The DEFRA leaflet "Managing Varroa" gives
a full account of the methods available for controlling Varroa in our bees. Every
beekeeper should have this leaflet! In it, the use of oxalic acid is referred to
and in Table 4 on page 21 it is shown that it is not approved in any EU state but
"tolerated" in many countries.
It should not be used when brood is present as they are damaged. This limits its
use to Dec/Jan and to times in the rest of the year when a colony is broodless. Some
of us have used it this winter, buying a prepared solution (3.5% oxalic acid in sugar
syrup) and following the instructions to dribble 5ml on each seam of bees. It was
effective, as there was an increase in drop of varroa after the treatment. I was
surprised to count about 300 from one of my colonies after 2 days and with about
another 100 a week later. I am glad they were not there to multiply up this Spring
on the new brood! Some beekeepers had no increased drop where their Varroa control
routines through the summer had been effective. There have been colony losses over
winter among those treated, but there is nothing to associate these deaths with the
use of oxalic acid. (The grapevine tells me that some beekeepers have experienced
quite high colony losses this year.)
Oxalic acid could be used to good effect during the summer when the bees are broodless.
Swarms collected could be routinely treated before they have brood, say when they
have been hived for 2-3 days. It would be wise to let them settle in rather than
treat them as soon as hived. The best time for this summer treatment would be in
the evening when flying has ceased. Artificial swarms could also be treated as long
as the treatment was applied when the colonies were broodless.
BEEVITAL HIVECLEAN is now available and it contains oxalic acid (among other things)
and is claimed to be effective against Varroa and is said to be safe to use when
there is brood present. Some may prefer to use this instead of oxalic acid.
As many have learned the hard way, it is essential to control Varroa in our colonies
and now that resistance has appeared it will be even more difficult. It is now more
important than it was before resistance appeared that we monitor the Varroa drop
throughout the season so that appropriate action can be taken at the correct time.
Do reread the DEFRA leaflet!
Bee-Lines (A selection from our quarterly magazine)