I just found this quoted from honeybeesuite.com:
HopGuard is a new pesticide designed to kill Varroa mites. Although the product is not yet registered with the Environmental Protection Agency (EPA), three states have joined together to request a Section 18 Emergency Exemption to use the product in honey bee hives within the boundaries of those states. The Washington State Department of Agriculture, the Idaho State Department of Agriculture, and the Oregon Department of Agriculture submitted the request to the EPA on August 23. Working with the three agencies is BetaTec Hop Products, the maker of HopGuard and a wholly owned subsidiary of John I. Haas, Inc. of Yakima.
Section 18 of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) allows an unregistered product to be used in certain regional areas when an emergency pest situation exists and there is no viable alternative method of control. The three states argue that the seven pesticides currently approved for use on Varroa mites in the region are either ineffective or impractical to control the mites in commercial hives.
So what is HopGuard? HopGuard is made from one of the organic acids found in the hop plant, Humulus lupulus. An organic acid is simply a carbon-containing compound with acidic properties. Some of the current Varroa treatments also use organic acids, including ApiLife Var and ApiGuard, both of which contain thymol (found in thyme) and MiteAway II, which contains formic acid (similar to that found in fire ants.)
Hops contain two prominent organic acids, alpha acids—known to brewers as “flavor” hops—and beta acids, known as “aroma” hops. It is the beta acids that have been found to have anti-Varroa properties.
The new formulation is 16% beta acids painted on cardboard strips which will be used in the brood boxes. Two strips per brood box will be used up to three times per year. Since the product contains only “Generally Recognized as Safe” (GRAS) ingredients, the manufacturer believes the product can be used in the hives anytime—even during a honey flow.
The manufacturer is seeking registration as a biopesticide (short for biochemical pesticide) which is the EPA term for a naturally-occurring pesticide.
Will it work? In my opinion, organic acids are excellent pesticides because of their safety to both bees and the planet. However, in the past they have received only moderate acceptance in the beekeeping community—mostly because daytime temperatures and the brood-rearing cycle must be closely monitored. In addition, the hives usually must be made into “fumigation chambers” for the organic acids to work properly. This is time-consuming and hard on the bees.
Will HopGuard be any different? Only time will tell. In my experience the thymol products have worked great. But since I am not a commercial beekeeper, I have the time and inclination to fiddle around with the exacting conditions that allow those products to be effective. If HopGuard is simpler to use, it could revolutionize mite control, but the jury is still out. More data are needed.