The Varroa Annual Plan: Timing Is Everything

In Varroa management, there is one factor more important than the choice of treatment product, more important than the dosage, and more important than the method: timing. A perfectly executed treatment at the wrong time achieves little, while a simple measure at the right time can make the decisive difference.

In this lesson, we guide you month by month through the Varroa year and show you when each measure is due -- and above all, why that particular window is so critical.

Why Timing Is So Critical

The Varroa mite reproduces exponentially. A colony that starts spring with 50 mites can easily harbour 5,000-10,000 mites by autumn without treatment. But the raw mite count is not the problem -- what matters is when the mite load becomes critical.

This is precisely why the main treatment must be completed before August or at least begun -- not only in September, when it may already be too late.

The Annual Overview

Detailed Monthly Plan

Winter (December -- February): Residual Mite Removal

The winter treatment is the cleanest cut in the Varroa year. In the brood-free phase, all mites sit on the bees and can be reached by oxalic acid.

December (ideally):

• Trickle oxalic acid 3.5 %, 5 ml per occupied frame gap
• Maximum 50 ml per colony
• Only during brood-free conditions (at least 3 weeks of frost beforehand)
• Single application -- repetition damages the bees!

January -- February:

• If the December treatment was not possible (mild weather, residual brood), it can be caught up in January
• Insert monitoring board and check natural mite drop
• From February: no more treatment -- the brood nest is being re-established

Spring (March -- May): Biotechnical Phase

In spring, brood rearing begins again -- and with it, Varroa mite reproduction. Now is the time for biotechnical measures that reduce the mite pressure without chemicals.

March:

• First spring inspection in mild weather (above 12 °C)
• Check monitoring board: natural mite drop gives a first indication
• Assess colony development: unite weak colonies

April:

• Insert drone frames: Hang an empty frame (or drone foundation frame) in the brood nest
• The bees build drone cells, the queen lays in them
• Varroa mites prefer drone brood 8-12 times more than worker brood!

May:

• Carry out drone brood removal: When the drone brood is capped (after approx. 24 days), remove the frame and cut out the brood
• Mites trapped in the drone brood are removed along with it
• Repeat 2-3 times per season (April to June)
• Start monitoring: Powdered sugar method or monitoring board

Summer (June -- August): The Decisive Phase

This is where the Varroa year is won or lost. The mite population grows exponentially, and you must perfectly time the transition from monitoring to active treatment.

June:

• Monitoring every 3-4 weeks (powdered sugar method or monitoring board)
• Watch the thresholds:
  • Powdered sugar method: over 3 mites per 100 bees = treatment needed
  • Monitoring board: over 5 mites per day = treatment needed
• Last drone brood removal still possible (final round)

July -- THE Key Month:

• Carry out the last honey harvest
• Immediately start formic acid long-term treatment (Nassenheider, 200 ml FA 60 %, 10-14 days)
• Alternative: begin thymol treatment (Apiguard, Thymovar) -- but this needs 4-6 weeks!
• Start feeding after FA treatment is complete (at least 3 days gap -- simultaneous feeding changes the acid's evaporation rate)

August:

• Summer treatment is running or completed
• For formic acid: check mite drop after 14 days of treatment
• If needed: second short-term treatment (sponge cloth, 3-5 days)
• Continue feeding (target: 15-20 kg winter stores)

Autumn (September -- November): Checking and Winter Preparation

September:

• Complete summer treatment
• Efficacy check: insert monitoring board for 3 days
  • Under 0.5 mites/day: Very good
  • 0.5-1 mite/day: Acceptable, continue monitoring
  • Over 1 mite/day: Consider follow-up treatment
• Complete autumn feeding by mid-September

October:

• Final monitoring of the season
• Winterise colonies: reduce entrance, fit mouse guards
• Check colony record book for completeness

November:

• Wait for a cold period
• After 3+ weeks of frost: brood-free conditions likely
• Plan timing for winter treatment

The Critical Window: July to September

If there is one section of this lesson to remember, it is this:

The three months July, August, and September determine the survival of your colonies next winter.

The reasons:

1. Exponential reproduction: The mite population doubles approximately every 3-4 weeks. What looked harmless in June can be catastrophic by August.

2. Winter bee rearing: From August, the long-lived winter bees are reared. Mite infestation during this phase shortens their lifespan and transmits viruses (DWV, ABPV).

3. Last treatment opportunity: After September, it is too cold for an effective summer treatment (formic acid needs above 15 °C, thymol likewise). The next chance is the winter treatment in December -- but by then the damage to winter bees is already done.

Winter losses are made in summer. If you have not started treatment by the end of July, you have essentially already lost the fight against Varroa -- regardless of how good the winter treatment later is.

Your Personal Varroa Annual Calendar

Reinvasion: The Underestimated Factor

Even if your treatment was perfect, reinvasion from the surrounding area can undo your success. Mites transfer between colonies via drifting bees, robbing, and drifting drones.

What to Do If You Are Running Late?

Not everything goes to plan. Here is an emergency roadmap:

Common Timing Mistakes

Knowledge Check

In the next lesson, we look to the future: Can we breed bees that defend themselves against Varroa? We explore VSH, SMR, and the most exciting breeding programmes.