The August varroa treatment, and why it is the one that counts

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The biology that sets the date

Brood normally peaks in July, and after that the brood population drops while the mite population keeps rising, because there is still plenty of brood to breed in. 1 So infestation can get high quickly in August - which is when the winter bees are developing.

Then the part that explains the winter losses. Varroa damages the fat body, and that damage can shorten the lives of winter bees. 1 Winter bees have to live for months rather than weeks, and they do it on those reserves. Heavy infestation during August therefore increases the risk of the colony collapsing over winter. Treat too late and the varroacide still kills mites, but it cannot undo the damage already done to the winter bees.

It also explains the shape of the loss. Mite damage done in August does not look like dead bees in August. It looks like a colony that thins out through November and December and is found dead in the new year, sometimes with stores still in the box.

When

Winter preparation starts once the last honey crop is off, and that is normally when the varroacide goes on: early to mid-August in most apiaries. 2 Later if you are on a late flow such as heather or Himalayan balsam.

Monitoring runs slightly ahead of that. The NBU is specific that monitoring in late July is important, precisely so you know mite levels are low before the winter bees start being raised in August. 1 Then check again in October - that tells you whether the late-summer treatment worked and whether a winter oxalic acid treatment is needed.

Choosing a treatment

The NBU’s position is that varroacides based on organic acids (oxalic, formic) or on thymol should be your first choice, because there are no reports of mites becoming resistant to them. The synthetic pyrethroid and amitraz products currently authorised in the UK - Apivar, Apitraz and Apistan - should be used sparingly and alternated with something else. 1

Whatever you pick, the label decides how you use it. As a worked example, Vita’s own Apiguard instructions say the external temperature should be above roughly 15 °C - and the reason is worth knowing, because it is not simple evaporation. The gel is distributed by the bees themselves as they clean the hive, and that activity increases as it gets warmer.

A cold snap does not just slow the bees down. It slows the whole treatment, because the bees are what move the gel around. Vita says Apiguard still works in cooler weather, but the mite kill is slower and the treatment takes longer. Apiguard is also meant to be used outside a honey flow, with supers preferably removed, over an ideal total of about six weeks. 3

Where the tray actually goes, what changes above 25 °C, and the different dose for a double brood box are a job of their own: putting the varroa treatment on.

Different products, different rules. Read yours.

Monitoring that means something

The NBU’s general guidance is to keep the population below roughly 1,000 mites in a colony to avoid serious damage, and it is worth being honest that estimating that from a drop count is approximate. 1 What matters more is consistency: pick one method, use it the same way each time, and compare your own numbers against each other rather than against a table.

A floor insert left in for a known number of days gives you a daily natural drop, though it is affected by weather, floor type and anything else on the board. Taking a sample of about 300 bees instead gives you mites per hundred bees and depends far less on conditions - but the two ways of doing it are not equivalent.

An alcohol wash is the more reliable and the one to use when you want a number you can trust; it also kills the sampled bees, which is worth knowing before you start. A sugar roll spares them but can under-report, so a low sugar-roll result is weaker evidence than a low wash.

Whichever you pick, monitor colonies systematically and ideally across the whole apiary at once. Mite loads vary between colonies in the same apiary, and an untreated hive next door will reinfest a treated one through drifting and robbing.

The order to work in

1. Take the crop you are taking. Most products are not for use with harvest supers on, and honey taken during treatment or its withdrawal period should not be sold or eaten.
2. Monitor - late July.
3. Treat, on the label, while it is warm enough for the product to work.
4. Feed. Note that feeding while a varroacide is in the hive may not be advisable depending on the product, so check the label for that too. See Autumn feeding.
5. Monitor again in October and decide about a winter treatment.

The records you have to keep

Varroa treatments are veterinary medicines, so the product, supplier, date, dose, batch number and disposal all have to be recorded and kept for five years - whether or not you sell any honey. The beekeeper’s veterinary medicines record sets out exactly what goes in it.

One date deserves singling out. The withdrawal period is set by the product, and GOV.UK lists it among the things you record when you treat. 4 So read it off the label rather than assuming.

In practice that means you need both dates: when the medicine went in, and when it came out. Write the removal date down when you pull the strips, rather than trying to remember it in November. And do not harvest until the period on the label has passed.

Varroa is also reportable on BeeBase, which is a different duty from the notifiable diseases and takes about a minute - the difference between the two.

Smoke, and how much of it to use while you work, is in Lighting and managing a smoker.

The treatment goes on once the crop is off, so getting the bees out of the supers comes first, and having the product in before August comes before that.