Thank you for reaching out with this beekeeping question!

Unfortunately, we hope that most of the needed varroa mite management was already done earlier in the beekeeping season. Varroa mite levels are usually at low levels in the spring, and they build up in population through the summer and fall. As varroa mite loads increase, virus levels also increase. We attribute a lot of colony losses in the winter to these viruses. Colonies with winter bees that develop in the fall under high virus pressure may be unable to survive.

We recommend that beekeepers keep varroa mite levels throughout the beekeeping season to keep virus levels low. Even if a treatment done now/soon kills a lot of varroa mites, we expect the virus levels in the colony to remain high for several weeks or months.

Our team discusses varroa mite management throughout the season in our Michigan Beekeeping Webinar Office Hours. Here is a link to the recordings: Michigan State University Beekeeping - YouTube.

As an example, our colonies at MSU received varroa mite treatments this spring and summer. We want to avoid treatments now (in October) because colonies will begin clustering as temperatures drop, and some treatments can disrupt colonies. At MSU, we usually do an oxalic acid dribble (solution method) in November or December when we expect colonies to be broodless. The oxalic acid treatment is most effective when mites are exposed on adult bees (when they aren't in sealed brood). The idea behind this winter treatment is more to kill mites overwintering in colonies for the next season, not to try to make a difference in colonies overwintering this year (since most of the damage of viruses may already be done).

Here is a list from EPA of approved treatments: EPA-registered Pesticide Products Approved for Use Against Varroa Mites in Bee Hives | US EPA. You can read EPA pesticide labels for relevant restrictions or recommendations regarding temperature during the application period. I also recommend paying extra attention to the treatment period (length). Some beekeepers apply Apiguard or Api Life Var in the fall after pulling honey supers, so you could consider those treatments.

Happy beekeeping!

Hello.  I wanted to let you know I truly appreciate having this as a resource.  I have reached out a few times in the past year which was my first year beekeeping.  I joined my husband who has been beekeeping for a few years.  I appreciate how the answers always address what was asked, and provide insight/background to teach.  I also appreciate always having links and other resources provided.  I have learned a lot in the past year and hope to improve on my skills.  Thank-you for all you do!

Thank you very much for taking the time to write a nice note! It's great to know when our work is appreciated. 

We appreciate you and other beekeepers in Michigan who make efforts to learn about beekeeping and ask good questions!

Happy beekeeping!