When to Treat for Varroa Mites

Varroa mites are small parasites that feed on the fat bodies of bees and weaken your colony. Treating at the right time makes the difference between a thriving hive and a dead-out. The goal is to hit mites when the colony is vulnerable and before they multiply out of control.

Spring Treatment Timing

Spring treatment depends on your local climate and what happened over winter. If you treated in fall, you may not need spring treatment—but check your hive first. In early spring (when daytime temps reach 50°F consistently), open the hive on a warm day and do a mite count. Two reliable methods are the alcohol wash (a measured sample of bees is submerged in alcohol to dislodge and count mites) and the powdered sugar shake (bees are shaken with powdered sugar, which causes mites to fall off onto a white surface for counting). If you find more than 3–5 mites per 100 bees, treatment is justified.

The tricky part: spring is when the colony is rebuilding. A stressed hive can fail even if it survived winter. Use gentler treatments in spring—formic acid (an organic acid that vaporizes and penetrates brood cells) or oxalic acid (another organic acid, typically applied by vaporization or drizzle) work well because they break down naturally and don’t leave residues. Note that specific products containing these acids may require a license or prescription depending on your country or state, so check local regulations before purchasing. Avoid synthetic miticides like fluvalinate (sold as Apistan, a plastic strip placed in the hive) or coumaphos (sold as CheckMite+, also a strip treatment) in spring; they can stress a recovering colony.

Timing matters. Treat too early (late February in cold climates) and the colony is still small, so mites are concentrated and easier to kill—but cold weather limits treatment options. Treat in mid-April and the colony is stronger, but mites have already started multiplying on the expanding brood. Most beekeepers find late March to mid-April is the sweet spot: weather is warming, the colony is growing, and you can use multiple treatment types.

Don’t treat during a nectar flow if you can help it. If spring flowers are blooming and bees are bringing in pollen and nectar, wait. Treatments can stress bees and reduce foraging. If mite counts are very high (over 10 per 100 bees), treat anyway—a dead hive won’t make honey.

Late-Summer/Fall Treatment Timing

Fall treatment is the most important one. This is when mites peak, and a heavy infestation now means a weak or dead colony next spring. Start monitoring in late July or early August. Do mite counts every two weeks. When you hit 5–8 mites per 100 bees, it’s time to act.

The window is tight. You need to treat after the main honey flow ends (so you don’t contaminate honey) but before brood production slows down too much (so treatments are effective). In most regions, this means late August through September. Treat too late—say, November—and the colony has already suffered heavy mite damage. The bees are weakened, and even if you kill the mites, the colony may not survive winter.

Synthetic miticides like fluvalinate (Apistan) and coumaphos (CheckMite+) are effective in fall, but only if your mites aren’t resistant. Many regions now have resistant mite populations, so check with local beekeepers or your extension office first. If resistance is a problem, use formic acid or oxalic acid instead. As with spring treatments, confirm which products are legally available in your area before use.

Oxalic acid is popular in fall because it’s affordable, effective, and breaks down completely. Apply it when brood is minimal—late September through October works in most climates. The timing is critical: oxalic acid doesn’t penetrate sealed brood cells, so it only kills mites on adult bees. Treat too early when there’s lots of brood, and you’ll miss mites hiding in cells.

After treatment, wait 2–3 weeks and do another mite count. If counts are still high, consult the product label and your local extension service before retreating, as re-treatment protocols vary by product. Remove any mite treatments before winter so bees aren’t exposed to chemicals during the long cluster period.

Emergency Treatment Signs

Sometimes you don’t have the luxury of waiting for the calendar. Certain signs mean you need to treat immediately, even outside normal timing windows.

Spotty brood pattern is a red flag. If you see empty cells scattered through the brood nest (not in a clean pattern), mites may be killing pupae. Healthy brood looks solid and uniform. Spotty brood means mites are winning.

Deformed wings are a sure sign of high mite pressure. If you see bees with crinkled, stunted wings, the colony has been infested for weeks. Treat now. These bees won’t live long, and the colony is in trouble.

Crawling bees—adults that can’t fly and crawl around the hive entrance or on the ground— indicate viral infections spread by mites. This is late-stage infestation. Treat immediately, though the colony may not recover.

Sudden population drop in late summer is suspicious. If a hive that looked strong in July is half the size by August, mites are likely the culprit. Check for mites and treat.

If you observe bees abandoning the hive in late summer, do a mite count immediately. If counts are high, treat any remaining bees and assess whether the colony is salvageable.

Treatment Timing Around Honey Supers

Never treat while honey supers are on the hive. Honey supers are the boxes placed above the main hive body where bees store surplus honey for harvest. Treatments can contaminate honey meant for human consumption. Remove supers before any treatment, wait for the treatment to work and clear, then put supers back on.

In spring, don’t put supers on until at least 2–3 weeks after treatment. In fall, remove supers before August or early September treatment. If you harvest honey in mid-August and want to treat, wait until supers are off and cleaned up. The delay is worth it—contaminated honey is a liability and a waste.

If you’re running a split or cutout and mite counts are high before the main flow, treat before you add supers. It’s better to delay honey production one year than to lose the colony.