Late Summer Varroa Mite Treatment: A Beginner's Essential Guide

As summer winds down and your bees begin preparing for winter (Yes, it's still warm out, but winter prep has begun!) there's one critical task that can make the difference between a thriving hive and colony collapse: treating for varroa mites. If you're new to beekeeping, varroa mite management might seem overwhelming, but understanding why, when, and how to treat these parasites is essential for your bees' survival.

Why Late Summer Treatment is Critical

Varroa mites (Varroa destructor) are tiny parasites that feed on the honey bee's fat body and reproduce in brood cells. While they're present year-round, their population explodes during summer, making late summer treatment absolutely crucial for several reasons:

Protecting Winter Bees: The bees born in late summer and early fall are your colony's winter survivors. These bees need to live for months, not weeks, to carry the colony through to spring. Varroa-weakened bees simply cannot survive the long winter months and produce the heat needed to keep the hive warm.

Breaking the Reproduction Cycle: Mites reproduce in sealed brood cells, with each female mite potentially producing 2-3 offspring. By late summer, mite populations have grown exponentially throughout the season. Treatment now prevents this population from overwhelming your colony.

Preventing Viral Transmission: Varroa mites are vectors for deadly viruses like Deformed Wing Virus and Black Queen Cell Virus. Heavy mite loads lead to virus outbreaks that can kill colonies rapidly.

Timing Before Cluster Formation: Once bees form their winter cluster, treatment options become limited. Late summer treatment ensures you address the problem while bees are still active and accessible.

Major Treatment Options: Pros, Cons, and Application Methods

1. Apiguard (Thymol-Based)

What it is: A thymol-based gel that comes in ready-to-use trays or tubs.

Pros:

• Easy to apply
• Natural essential oil base considered organic in the European Union (but not by the EPA)
• Long shelf life
• No withdrawal period needed (meaning you can put honey supers on the hive immediately after taking Apiguard out of the beehive)
• Can be in the hive when outside temperatures are between 60-105F

Cons:

• Temperature sensitive
• Cannot be used during a honey flow or when honey supers are on the hive
• Need to have an empty super around treatment (requires an extra box)
• Can slow egg laying temporarily
• Takes 4-6 weeks for full treatment (does not penetrate through brood cells)
• Strong odor that some bees dislike initially
• Can cause hives to abscond especially in high heat or improper dosage

How to Apply:

1. Remove honey supers before treatment
2. Peel the foil top off the 50g tray
3. Place the tray on top of the brood frames in the upper brood box
4. Replace after 2 weeks with a second tray
5. Ensure adequate ventilation in the hive
6. Remove empty trays after treatment completion

Note! If a hive is just one brood box or outside temperatures are above 77F, use a half dosage by cutting the tray in half and replacing every week or whenever the tray is empty or all dried up.

3. Formic Acid Treatments (Mite Away Quick Strips/Formic Pro)

What it is: Formic acid absorbed in gel pads or cardboard strips.

Pros:

• Kills mites under brood cappings
• Can be used during honey flow (check label)
• Organic approved
• Relatively quick treatment (7-14 days)
• No resistance issues reported

Cons:

• Very temperature sensitive (65-85°F optimal)
• Can kill queens or cause supersedure in weak colonies
• Requires precise application
• Can be harsh on bees in hot weather
• Caustic to human skin and eyes
• Cannot be used in small or weak hives

How to Apply:

1. Check temperature requirements carefully
2. Place strips on top bars of frames containing brood
3. Follow manufacturer's instructions exactly for number of strips
4. Ensure adequate ventilation
5. Remove strips after treatment period
6. Monitor colony closely during treatment

Formic acid is a very popular treatment to use during the late summer. Although it has temperature restrictions, the beekeeper is usually able to find a 3-4 day window in which temperatures are cool enough to put in the hive. Although directions state to leave in hive for 2 weeks, a 4 day window will kill a high percentage of mites since it fumigates the entire hive, including penetrating the beeswax capping over the developing bees.

4. Oxalic Acid (VarroxSan/Api-Bioxal)

What it is: Oxalic acid applied via vaporization, dribble, or slow-release strips.

Pros:

• Highly effective on phoretic (non-brood) mites
• Inexpensive
• Natural organic acid
• Multiple application methods
• Quick treatment time for vaporization
• Can be used with honey supers on the hive (or take off temporarily while putting treatment in if using the dribble method or vaporizer)
• Not temperature sensitive

Cons:

• Only kills mites on adult bees, not in brood
• Requires specialized equipment for vaporization
• Multiple treatments needed for effectiveness when brood is present (unless using varoxxsan strips)
• Safety equipment required

How to Apply:

• Vaporization: Requires specialized vaporizer, protective equipment, and sealed hive
• Dribble: Mix with sugar syrup and dribble between frames of clustered bees
• Strips: Place slow-release strips in hive according to manufacturer instructions
• Best applied when little to no brood is present

My Treatment Schedule

A successful late summer treatment plan should begin in August and continue into early fall:

July: Begin monitoring mite levels with alcohol washes. If mite counts exceed 2-3 mites per 100 bees, treatment is needed after honey has been harvested using formic acid for a few days when temperatures are in the low 80s.

October: Treat with oxalic acid before closing hive up for winter.

Safety and Best Practices

Always read and follow label instructions for any treatment product. Each has specific requirements for temperature, timing, and application methods.

Wear appropriate protective equipment, especially when handling formic acid or vaporizing oxalic acid. These chemicals can cause serious injury.

Remove honey supers before treating unless the product label specifically allows use during honey flow.

Monitor your colonies during and after treatment. Some treatments can stress colonies, particularly weak ones.

Keep treatment records including dates, products used, weather conditions, and colony responses. This information is invaluable for future treatment decisions.

Rotate treatment types annually to prevent resistance development, particularly with synthetic miticides.

Common Beginner Mistakes to Avoid

Treating too late: Waiting until October means treating bees that are already preparing for winter. These older bees may not survive long enough to benefit from treatment.

Skipping post-treatment monitoring: Always check that your treatment worked. A failed treatment is worse than no treatment because it gives false confidence.

Using expired products: Check expiration dates and storage requirements. Old or improperly stored treatments may be ineffective.

Inadequate ventilation: Most treatments require good air circulation. Poor ventilation can make treatments less effective or harm bees.

One-size-fits-all approach: Different colonies may need different treatments based on strength, mite levels, and local conditions.

Conclusion

Late summer varroa mite treatment is not optional—it's essential for colony survival. While the array of treatment options might seem overwhelming, each has its place in an integrated pest management approach. 

Remember that successful beekeeping is about working with your bees' natural cycles. By treating for varroa mites in late summer, you're giving your colonies the best possible chance to build strong, healthy winter populations that will emerge ready to thrive in spring.

The investment in time and money for varroa treatment pays dividends in colony survival and honey production. Your future self—and your bees—will thank you for taking this critical step in late summer hive management.