Verroa Mites: The Importance of Testing and Treating in September

As summer winds down and colonies prepare for winter, one of the greatest threats to honey bee health becomes more dangerous: Varroa mites. These tiny parasites, reddish-brown in color, attach to bees and feed on their fat bodies, weakening individual bees while also transmitting viruses that can devastate entire colonies. For beekeepers, September is a critical month to test and treat for Varroa mites to ensure colonies are strong and healthy heading into fall and winter.

Why Testing Matters

Testing isn’t optional—it’s essential. Varroa mites can build up silently, with colonies appearing healthy until suddenly collapsing. By the time visual symptoms show (such as deformed wings or dwindling populations), the infestation is often severe. Regular testing allows beekeepers to understand the mite load and act before it reaches harmful levels.

Two of the most reliable methods for testing are the alcohol wash and the sugar roll. Both involve collecting a small sample of bees, dislodging mites from their bodies, and counting the number present. The alcohol wash, though lethal to the sampled bees, provides the most accurate results. A threshold of around 2–3 mites per 100 bees often signals the need for immediate treatment. Without testing, beekeepers are left guessing—something too risky when winter survival is on the line.

Alcohol wash test with bees mites visible in the solution

Why September Is Critical

Fall bees are the workforce that carries the colony through the winter. These bees are physiologically different from summer bees: they live longer, conserve energy, and must remain healthy to sustain the cluster until spring. High mite levels in September shorten their lifespan, weaken their immune systems, and make them more susceptible to viruses like Deformed Wing Virus (DWV).

If mite infestations go unchecked now, colonies may dwindle rapidly over winter or even collapse entirely before spring. By testing and treating in September, beekeepers give colonies the best chance to survive the cold months ahead.

Treatment Options

Once testing confirms elevated mite levels, treatment becomes the next step.

Chemical treatments like formic acid, oxalic acid, or thymol, which are applied according to product directions and temperature ranges.

The key is to match the treatment to the season and colony condition. For example, oxalic acid treatments are most effective when colonies are broodless, often later in fall.

Varroa mite visible on a honey bee

Final Thoughts

September is not the time to take chances with Varroa. By testing colonies and treating when thresholds are exceeded, beekeepers safeguard their bees, reduce stress on colonies, and improve overwintering success rates. Healthy fall bees lead to thriving spring colonies, and the effort put in now can mean the difference between loss and growth in the coming season.

Testing and treating for Varroa mites this month is more than good practice—it’s the foundation for sustainable beekeeping.