Gardeners, Take Heed: It’s a ‘Tick-y Year’

This year, it will be hard to avoid ticks if you’re spending a lot of time outdoors. Here’s how to keep that from interfering with your gardening.

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Substantial chunks of my many growing seasons have been spent on maintenance, crawling around under shrubs and trees, weeding and pruning, dividing and deadheading. And because self-maintenance is part of garden success, too, between those sessions in the leaf litter — a prime tick habitat — I make it a practice to keep up with the latest tick research.

Various active studies continue to explore tactics for reducing tick encounters and disease transmission to humans. Until we know more, however, preventing tick-borne illness remains a matter of personal responsibility — not something an outside force will magically solve.

That means there is no substitute for vigilance, especially in “a tick-y year,” as Richard S. Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies, in Millbrook, N.Y., described 2021. And especially now, as populations of nymphal blacklegged ticks — Ixodes scapularis, often referred to as deer ticks — are peaking in the Northeast.

It’s an occupational hazard: While conducting fieldwork, tick researchers like Dr. Ostfeld cannot avail themselves of repellents or treated clothing — two powerful prevention tactics, along with diligent tick checks, of clothing, skin and scalp. But they urge us to use all three strategies, as they do in their own gardens.

“Lacking super-good diagnostic tools and effective disease treatments, or effective yard treatments that reduce risk, we don’t really have much yet,” said Dr. Ostfeld, who has been studying the ecology of Lyme and other tick-borne diseases for more than 30 years. “What we do have are ways of protecting ourselves, and most studies show that people who protect themselves are much less likely to get a tick bite that leads to disease.”

“It has to become like fastening your seatbelt, or putting on a helmet when riding a bike,” said Neeta P. Connally, a medical entomologist at Western Connecticut State University, in Danbury, where tick-monitoring research is in its 11th year. “It has to become a habit.”

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Heavy acorn crops like the one we had in 2019 provide food for rodents that can infect ticks with disease pathogens. “When you get a bumper acorn crop, two years later you get lots of infected blacklegged tick nymphs,” Dr. Ostfeld said.Credit…Cary Institute of Ecosystem Studies

It’s Not the Weather, It’s the Food Web

Casual accounts often blame abundant populations of ticks on a warm winter — fewer ticks were killed off, the speculation goes — or on a warm or early spring.

But “there is no simple relationship between recent weather and tick abundance,” Dr. Ostfeld said. “Weather factors aren’t very good at predicting whether any given year will be very tick-y or less tick-y.”

Acorns, it turns out, are a better forecasting tool.

“When you get a bumper acorn crop, two years later you get lots of infected blacklegged tick nymphs,” Dr. Ostfeld said.

And in 2019, we had a mast year — a heavy production of seeds that provide food for many animals, including rodents like white-footed mice.

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Well-fed mice have a population boom the summer after a heavy acorn crop, in time to provide a blood meal for a new generation of larval ticks that hatch from eggs in August or September.Credit…Cary Institute of Ecosystem Studies

Those well-fed mice have a population boom the following summer, in time to provide a blood meal for a generation of larval ticks that hatch from eggs around August or September. With that meal of rodent blood, the ticks, which were born uninfected, may also ingest pathogens that cause Lyme and other tick-borne diseases from the mice, and from eastern chipmunks.

Another population driver: Ticks that take their blood meal from a mouse have a high rate of not just infection, but also survival, compared with those that bite an opossum or another animal that grooms off and kills ticks more effectively.

The second year — where we are now — sees an abundance of infected, poppy-seed-size nymphs emerge. And our risk goes way up, Dr. Ostfeld said, as that’s the stage most responsible for transmitting disease.

Weather does affect tick behavior, including how much time they spend in an activity known as “questing,” which can be affected by humidity and temperature. Ticks cannot fly or jump; instead, they grip foliage with their lower two pair of legs and stretch out the top two pair, waiting to grab a host animal as it passes by.

“A long dry spell can reduce questing behavior,” Dr. Ostfeld said, “but might not kill off many ticks, so that a rainfall event brings them out in droves.”

Who knows what is causing the current surge in American dog ticks (Dermacentor variabilis) that I couldn’t wait to ask about. Dr. Ostfeld has a hypothesis: chipmunks. Dog tick nymphs love to bite chipmunks, he said, and last year was a bumper chipmunk year — after all those 2019 acorns fed them, too. The well-fed 2020 nymphs may now be reappearing as adults in large numbers.

One late May afternoon, Dr. Connally swiped her “tick flag” — fabric attached to a pole, used for sampling — along the brushy edge of a soccer field while watching her daughter’s game. In just two 30-second samples, she collected 43 adult dog ticks.

“Actually, there were more,” she said. “But I couldn’t grab them all before they crawled away.”

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Once a blacklegged tick hatches from an egg, it goes through several life stages, requiring a blood meal at each one: The nearly invisible spec at the bottom is a tiny larval tick; above it is a nymph, the stage most responsible for transmitting disease; and the two ticks at the top are an adult female and male.Credit…Cary Institute of Ecosystem Studies

Backyard Research

Blacklegged tick disease in humans is often contracted close to home, in backyards and neighborhoods. Various multiyear research projects past and present seek to reduce that risk — among them, The Tick Project, at Cary Institute, in collaboration with Bard College, and the Backyard Integrated Tick Management Study, at Western Connecticut State University.

In such studies, properties may be sprayed with substances poisonous to ticks. Another intervention, used separately or in combination with spraying: Bait boxes are set out to attract rodents, which rub against wicks inside treated with permethrin or fipronil, tick-killing ingredients also used in preventive pet products.

In controlled, small-scale experiments, these tactics have shown promise in reducing tick populations and the rate of infected ticks. But when they’re scaled up to whole neighborhoods, they may not work as well — and they don’t reduce bites or disease.

Beyond the backyard, other research focuses on deer, which do not infect ticks with pathogens, but are a culprit in their spread. Deer move around widely, bringing large numbers of ticks along with them.

One tool being used to combat this is a four-poster device — a stand containing a hopper of corn as bait. To get the bait, deer must rub their heads and necks on permethrin-impregnated rollers. This reduces the tick population, but with the cost and maintenance required, it is unclear if it is a widely applicable solution.

Ticks vs. How We Garden

We would probably have to stop gardening altogether to comply with the C.D.C. guidance on preventing tick bites: “Avoid wooded and brushy areas with high grass and leaf litter.”

And some ecologically minded garden practices may actually foster more tick habitat. My commitment to a less-fastidious fall cleanup to support successful overwintering by many beneficial insects and other arthropods, for example, means more leaf litter that harbors ticks. A study published in the Journal of Medical Entomology in 2020 — on fall leaf-blowing and raking in residential New Jersey properties that resulted in deeper litter buildup at property edges — seems to confirm that.

I won’t cart leaves to a municipal composting site or erase looser, wilder garden areas managed in the name of biodiversity. But I recognize the risks, and I know I must turn up the vigilance.

One positive note: The deer fence I put up years ago around the property, seeking to stop destructive herbivory, probably works in my favor. Still, I must not let that make me complacent.

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TheTickSuit, a breathable cotton jumpsuit, was developed by Joan Reibman, a doctor and professor at the N.Y.U. Grossman School of Medicine who gardens in Suffolk County, after she contracted Lyme disease.Credit…Barnet Kellman

Before Heading Out …

You know the drill: Wear light-colored clothing, so ticks are easier to spot; tuck your pants into your socks and your shirt into your pants.

I’m also thinking of investing in TheTickSuit. A breathable cotton jumpsuit with stirrups and thumb holes to keep you covered and a removable hood, it was developed by Joan Reibman, a doctor at N.Y.U. Langone medical center and a professor at the N.Y.U. Grossman School of Medicine. When Dr. Reibman, who gardens in Suffolk County, contracted Lyme disease, she was unwilling to give up gardening but unable to find the protective gear she needed. So she made it herself.

The suit — like most any clothing — can be sprayed with permethrin for additional protection. When applied at home, it lasts about six washes before it needs to be reapplied. Clothing can also be sent to Insect Shield for professional application, which is said to last five times longer. Ready-made pretreated clothing, from socks to whole outfits, is another option.

As are repellent sprays. Natural products might be effective, but they have not been well studied, said Dr. Connally, who recommends using E.P.A.-registered products that contain active ingredients like Picaridin or Deet (an E.P.A. search tool can help identify the right one). That is especially important this year, when the number of blacklegged nymphs that Dr. Connally recorded in her local monitoring project in the first week of June was 85 percent higher than the number she recorded during the same week in 2020, and 47 higher than in 2019.

Once you’ve finished gardening, don’t wear your garden clothes back indoors — not even if you’re just taking a short break for lunch. Washing them immediately helps, but only if the water is above 130 degrees. Much better, according to a 2016 study published in the journal Ticks and Tick-borne Diseases, is putting garments straight into the dryer on high for six minutes (or 10 minutes, per the C.D.C.), without washing them first.

Next: A shower within two hours of outdoor activity, following a thorough body check. And then one last self-check before bed.

And those indoor-outdoor pets? They need checking all the time. Just as we do.

Margaret Roach is creator of the website and podcast A Way to Garden, and a book of the same name.

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