Summer Treatments for Varroa Mites: A Few Good (or Okay) Choices

In any season, choosing the best Varroa destructor mite treatment requires some thought. In summer, however, it is complicated because most beekeepers have honey supers on our hives to collect honey for human consumption, which eliminates some options for food safety reasons. Explore our guide to learn what varroa mite treatments are suitable when honey supers are on, when to apply each treatment, and which option is best for your apiary.

Varroa mite treatment options for summer use

The treatment you choose depends on a few factors, including mite counts and time of year. Complete regular mite counts to keep an eye on mite populations, to help determine your ideal treatment schedule. If your mite levels are low, you won’t need to treat in the heat of summer. If they’re high, you need to find a suitable treatment or your bees’ health will suffer.

Though there are numerous mite treatment options for fall, three types of mite treatments are suitable for summer use. These include:

• Formic acid (e.g. Formic Pro)
• Oxalic acid
  • Dribbled or vaporized (e.g. Api-Bioxal, or EZ-OX)
  • Extended-release strips (e.g. VarroxSan)
• Hops beta acids (e.g. HopGuard III)

Keep in mind that these treatments aren’t one-size-fits-all! Before choosing a summer mite treatment, explore the pros and cons of each and determine which is the best option for your hives. Evaluate which solution will fit your needs using this information about the three summertime mite treatment options. And remember that miticides are regulated at both the federal and state level in the U.S., so it’s possible some miticides may not be available in your state.

Formic Pro

Of the three miticides recommended for summer use, formic acid (available commercially as Formic Pro) is the summer mite management mainstay because it has two important features:

• It can be used when honey supers are in place
• It kills varroa mites under brood cappings, meaning all of the varroa in the hive are vulnerable to it

However, Formic Pro has one important downside: There is an upper limit on the maximum outside air temperatures during the first few days of the 2-week long treatment period. Ideal daily air temperature maximums are between 50 to 85 degrees F, and temperatures above 92 degrees F in the first three days may result in significant brood, bee, or even queen loss. In areas of the US where summer daily highs remain well above 85 F for weeks on end, Formic Pro is not a suitable treatment option. But in many areas, it is possible to find a slightly cooler week to get this treatment underway. 

A full-sized standard Langstroth hive can be treated with two Formic Pro pads at once, or an alternate treatment method is permitted that involves applying the pads one at a time with 10 days between applications. Both methods kill mites, though the 2-pad, 14-day treatment penetrates brood caps and kills mites in the brood more effectively. However, the 1-pad + 1-pad-10-days-later method releases less formic acid at once, and may be slightly gentler on the bees when the thermometer is flirting with the upper temperature limit for Formic Pro treatment.

Treatment length: 14- and 20-day treatment options.

Oxalic Acid

Another summer treatment option is dribbled or vaporized oxalic acid, sold as Api-Bioxal and EZ-OX, neither of which are approved in every state. These oxalic acid products have no upper air temperature limit, making them useful for hot summer days. However, the dribbled or vaporized oxalic acid does not kill varroa protected under the cappings. Oxalic acid was formerly forbidden from use with supers on the hive, but that restriction was lifted in 2021 after research showed the risks of honey contamination were not significant (since oxalic acid from plant nectar can naturally occur in honey anyway).

During any period of broodlessness, a single treatment of oxalic acid may provide excellent varroa control. It can be applied in the form of a sugar-syrup mixture which is dribbled onto the surface of the frames or heated in a specialized device, like the Varrox Oxalic Acid Vaporizer or ProVap Bee Vaporizer, with the resulting plume of tiny crystals retained inside the hive.

From time to time, a summer colony may have little to no brood for mites to hide in, making oxalic acid a great treatment. An excellent and effective summer use of oxalic acid vaporization is after a new swarm has been hived and settled in, but before there is any capped brood. Any period of broodlessness should be considered as a potential opportunity for a quick oxalic acid treatment. Even in a hive with brood, a short series of vaporizations may be useful, though significantly less effective, than when capped brood is entirely absent.

Treatment length: After the initial flash treatment, dead mites will fall from the bees for 24 to 36 hours. Repeat treatments may be of moderate use between 3 to 7 days later. 

A completely new option is just arriving in the U.S., and we’re excited to see how it works in our hives and yours. An extended-release oxalic acid strip product called VarroxSan has been approved in the U.S. and is rapidly being approved by each state. By August of this year, we expect to be shipping the first packages of VarroxSan strips out to the beekeepers on our waiting list. These fiberboard strips are soaked in oxalic acid, glycerin, and other compounds that cause a slow release of oxalic acid into the hive over the treatment period. The ongoing research on this product (and similar products) suggests that it’s good at keeping mite levels from growing, but it’s not nearly as good at quickly knocking them down.  So if your mite levels are low or moderate, an extended-release strip may be able to keep the levels low. If your mite levels are high, another product is probably a better choice for your bees. 

Treatment length: After inserting the strips into your hive, they should be left in place for 42-56 days for a long-term exposure of the bees and mites to the oxalic acid.

Hops Beta Acids

Another option for summer, HopGuard III, also allows the honey supers to be in place during the treatment period. However, it is not as useful as Formic Pro because it doesn’t kill varroa mites protected under brood cappings. HopGuard III is useful when a colony has little to no brood, but is less valuable for a colony full of brood. Repeated applications of HopGuard III to try to “catch” mites emerging from brood are permitted, but not extremely effective. On the other hand, its high-temperature limit is 92 degrees F compared to Formic Pro’s 85 degree limit, making it a possible choice in areas where daytime temperatures prevent the use of formic acid. The active ingredient is food-safe for honey supers, because it comes from the hop plant, the same plant that is used to flavor beer. (Beer, however, is not effective against mites and is best reserved for the beekeeper instead!)

Treatment length: 14- to 30-day treatment duration, can be repeated up to three times per year.

Summer mite treatment is an important consideration for beekeepers to reduce varroa populations and improve colony outcomes. However, with summer’s supers and brood, you must choose the correct treatment option. Formic Pro, HopGuard III, and various oxalic acid products are often suitable choices if your hives meet the requirements for use. For more beekeeping tips, explore our Guide to Beekeeping.