Autumn Varroa Treatment: The Right Timing

The varroa mite remains the greatest threat to our bee colonies. A consistent autumn treatment determines whether your colonies make it through winter healthy. In this article, you'll learn when and how to proceed most effectively.

Why Is the Autumn Treatment So Important?

From late August onward, the so-called winter bees emerge. These bees need to survive until the following spring — six months or longer. If they're damaged by varroa, they won't make it through winter. This means: treatment must be completed before the winter bees emerge.

As a rule of thumb: the main treatment should be completed by end of August. The final mite cleanup with oxalic acid then takes place during the broodless period in December or January.

Method 1: Formic Acid (60%) in August

Formic acid is the treatment of choice for the summer treatment, as it is the only approved substance that also works inside capped brood. Formic acid 60% (veterinary grade) is used with approved evaporators (Nassenheider Professional, Liebig dispenser, or Formic Pro strips).

Long-Term Treatment with Evaporator

• Period: Late July to mid-August (latest early September)
• Temperature window: 15–25 degrees Celsius during the day (above 30 degrees, brood damage is possible!)
• Duration: 10–14 days, depending on evaporator type
• Dosage: Exactly according to evaporator manufacturer instructions and package insert (varies by evaporator type and box dimensions)
• Efficacy: 85–95 percent with correct application

Formic Pro Strips

Formic Pro strips are a newer, easy-to-apply method. Two strips are placed directly on the frames in the brood nest.

• Option 1: 2 strips for 14 days
• Option 2: 1 strip for 10 days, then replace with a second strip for another 10 days
• Temperature window: 10–29 degrees Celsius
• Efficacy: 83–97 percent according to the manufacturer

Application Tips

• Ensure sufficient entrance height for good ventilation (open mesh floor ideal)
• Do not treat at temperatures above 30 degrees — risk of brood damage and queen loss
• Check brood frames — with too much open brood, watch out for queen safety
• Food reserves should be present so bees don't starve under stress
• Start treatment in the morning or evening when temperatures are still moderate

Method 2: Thymol in August/September

Thymol-based products (Apiguard, Thymovar, ApiLife Var) are an alternative to formic acid, especially when the temperature window for formic acid doesn't fit.

• Temperature window: 15–30 degrees Celsius (optimal 20–25 degrees)
• Duration: 4–6 weeks (usually 2 applications at 14-day intervals)
• Efficacy: 85–95 percent at optimal temperatures
• Advantage: Simple application, fewer queen losses than with formic acid
• Disadvantage: Does not penetrate capped brood, possible flavor alteration in honey (apply only after the last honey harvest!)

Those who haven't treated their colonies by end of August lose the race against the mite. The winter bees emerging from September onward must be healthy — otherwise the colony is lost.

Method 3: Oxalic Acid in Winter

The oxalic acid treatment is the most important final mite cleanup. It only works on mites sitting on the bees — not in the brood.

The Perfect Timing

• When: 3–4 weeks after the first hard frost
• Condition: The colony must be broodless
• Typical: Mid-December to early January
• Temperature: Ideally below 5 degrees (bees are clustered)

Trickle Method

1. Prepare oxalic acid dihydrate solution (3.5 percent in sugar syrup)
2. Trickle 5 ml per occupied frame space
3. Maximum 50 ml per colony
4. Trickle method: Apply only once per winter (with vaporization, multiple applications may be permitted per the label)

Monitoring Treatment Success

After each treatment, you should monitor the natural mite drop:

• Under 1 mite per day in October: Colony is well supplied
• 1–5 mites per day: Watch carefully
• Over 5 mites per day: Retreat immediately

Don't Forget Documentation

Every treatment must be documented in the colony record book — date, substance, dosage, and colony. With Hivekraft, this happens directly at the apiary: enter the treatment, and the colony record book is automatically maintained. The Varroa documentation shows you infestation trends across the entire season, and the AI analysis recommends the optimal treatment timing.

Conclusion

The autumn treatment against varroa is the most important appointment in the beekeeping year. Plan early, monitor mite drop, and document every treatment. This is how you bring your colonies safely through winter.

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