Thresholds: when to treat

It's the third week of May. Anne does her first alcohol wash of the year and counts six mites. Six mites in three hundred bees is two per hundred. The colony looks wonderful, packed with brood and building fast. Does two per hundred matter in May? It does. And to see why, you need thresholds.

A threshold is the mite level at which you should act. Below it, you keep monitoring. Above it, you treat, or the mites will outgrow the colony before winter.

I need to be straight with you about something first. Ontario's agriculture ministry publishes thresholds on two different pages, and they don't agree. One says treat above two mites per hundred bees in spring and above three in August. The other, updated in May of twenty twenty six, says above one in spring and above two in August. This course uses the stricter numbers. They are safer, especially for beginners.

So here they are. With an alcohol wash in spring, around May, treat if you find more than one mite per hundred bees. In late summer, around August, treat if you find more than two per hundred.

If you use a sticky board instead, the stricter figures are more than three mites falling per day in spring, and more than nine per day in late summer.

And there is one deadline above all the others. Ontario guidance is to have mites below three percent by the first of October. That means sampling in the last week of August or the first week of September, and treating straight away if you need to. Don't wait. The winter bees are being raised right then, and they need to grow up in a hive with few mites.

Why does spring matter so much, if the deadline is October? Because mites multiply with the brood all summer. Two per hundred in May can become a serious number by August, when the colony is at its biggest and the brood is at its peak.

The Honey Bee Health Coalition, a North American group, works the same way. In the quiet, broodless part of the year it treats one percent as the trigger, and for most of the season, two to three percent.

After you treat, test again. If the count is still above three percent, the Honey Bee Health Coalition's guidance is to treat again with a different product, because the mites may be resistant to the first one.

Now let's change one fact. Suppose Anne gets the same count of two per hundred, but in the middle of October instead of May. Now the problem is different. The winter bees have already been raised with those mites. Treating still helps, but a lot of the damage is done. In Ontario, a count taken too late is almost as bad as none.

The mistake beginners make is treating by the calendar, or not treating at all because the colony looks strong. Let the count decide, and do it on time.

Here is the rule, in one breath. Using the stricter Ontario numbers, treat above one mite per hundred bees in spring and above two in late summer, test again after treating, and get every colony below three percent by the first of October.

Next, the treatments that are registered for use in Canada, and how to use them legally.