Acaricides: The Actual Tick Killers
An acaricide is anything made specifically to kill ticks and mites. That's different from a repellent, which just makes a tick want to steer clear of you.
Acaricides go after a tick's nervous system, its breathing, or its ability to molt and reproduce. The man-made ones flat out outperform the natural ones, and once you look at the numbers it's not really a close contest, even though that's not always what people want to hear.
Pyrethroids: Permethrin and Bifenthrin
Permethrin and bifenthrin are both synthetic pyrethroids, which just means they're a lab-made version of a compound that naturally shows up in chrysanthemum flowers. They overload a tick's nervous system until it can't function anymore, and that kills it on contact or shortly after.
Permethrin is what goes on clothing and gear. It bonds right into the fabric and holds up through a lot of washes, factory-treated stuff can go 70 washes before you need to treat it again. It's not really made for spraying the yard, though a few yard products do have it in there.
Bifenthrin is the one people reach for on the yard and the perimeter. It's the active stuff in Talstar and most of the professional pest control products. In testing, a single spray of it has wiped out nearly every nymph tick in the treated area for as long as 9 weeks afterward. It kills ticks dead even at pretty low concentrations. And it sticks around in the soil a bit longer than permethrin does, closer to a month versus permethrin's two weeks or so.
Natural Options: Rosemary, Peppermint, Clove, Cedar
These plant-based products are real, they're not nothing, but they're not in the same league as the chemical stuff and the numbers make that pretty clear. A CDC-funded test run out of the TickEncounter program at the University of Rhode Island took a bunch of natural products, cedar oil, rosemary oil, clove oil, and tried them against groups of deer ticks over a couple weeks, with bifenthrin thrown in as the benchmark. Bifenthrin wiped them all out, basically 100 percent, even a month later. Some of the natural stuff barely beat plain water. The best ones only got to around 30 percent. The guy running that study put it bluntly: if your product isn't killing at least 85 percent of the ticks, you're misleading people by calling it tick control.
That said, not every natural product is the same, and a couple have actually held their own in other tests. A rosemary and peppermint oil blend called Eco-Exempt IC2, when a professional sprayed it with proper high-pressure equipment, did about as well as bifenthrin for several months in trials run in Maine. The catch is how it gets put down. Professional high-pressure spraying got real results. The same kind of oil blend put down with an ordinary backyard pump sprayer in trials out of New Jersey only held up for one to three weeks and needed repeat treatments to stay even decent.