When is it Too Late to do an OAV Treatment?
Ask the Expert!
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Dave Curtis asks:
I completed the mite strip treatments a couple of weeks ago. Now I am wondering when should I start my OAV treatment. I am in Minnesota.
Rusty Burlew replies:
You can do OAV treatments any time during the year, including mid-winter. Oxalic vapor cannot penetrate the brood caps, so selecting a treatment time when the brood nest is small will give you the best results.
As a general rule, the amount of brood in a hive gets smaller and smaller until early January. At that time, brood rearing begins again, gradually at first, but at a steadily increasing rate. Remember, however, that every colony is an individual, so the perfect time will vary from hive to hive.
There is no easy way to determine when your particular brood nests are at their smallest other than inspecting the frames. Since that can be disturbing to the bees, most northern beekeepers simply use the calendar as a guide. November and December are good OAV treatment months because even if some brood is present, it will be a small amount, meaning not many varroa mites will be present under the caps.
Since you just finished a mite treatment, I think waiting until November or December would be prudent. Mite treatments can cause harm to bees, so it’s my preference to give them some time to recover between assaults. You can probably get away with doing OAV right after mite strips, but I think the treatment would be both safer and more efficacious if done closer to the end of the year.