Tick-Resistant Gardens

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by Mary Jasch

Deer-resistant gardens may be the latest craze in garden design, but why not stretch the horticultural – and health – envelopes with a Tick-Resistant Garden?

Consider that 75% of reported Lyme disease cases are contracted in residential back yards. And consider that 20,452 confirmed cases so far this year (by Center for Disease Control) in just five East Coast states equals 68% of the 29,959 cases nationwide - all this, despite the downturn in blacklegged (a.k.a. deer) tick activity this summer due to blistering temperatures and drought.

The concept and implementation of a tick-resistant garden fits snugly with the latest precepts in ecology-minded garden design – environmentally sound, native, anti-exotic, low maintenance once established. It goes beyond the complacent with a whole foods, whole earth, whole garden integrated approach.

2010 CDC Confirmed Lyme Disease Cases
CT – 2,751
NJ – 4,598
NY – 4,134
PA – 4,950
MA – 4,019
CA – 117 (Such a big state with so little disease. Read why in Tick Management Handbook)

Kirby Stafford III PhD, Vice Director, Chief and State Entomologist, Department of Entomology, The Connecticut Agricultural Experiment Station (CAES), New Haven, has been involved in tick research on many fronts for 23 years. His 84-page handbook Tick Management Handbook (TMH), is the definitive informational word on tick ecology, diseases, removal, repellants, and a complete and varied integrated approach to tick management for the property owner.

To effectively manage disease-causing ticks and to create a tick-resistant garden or property, a gardener must understand how the blacklegged tick lives.

It takes two years for Ixodes scapularis, a.k.a. blacklegged tick, to complete its lifecycle.

Females lay eggs in May. Eggs hatch into larvae July into early August and feed on mice, chipmunks and birds – many infected. They drop off and molt to nymphs, over-winter, and appear the following spring with May, June and July being the peak months for nymphal activity. They appear before newly hatched larvae and feed on rodents and birds – many already infected and others that they now infect. Nymphs molt to adults that feed on large mammals including deer, humans and pets. Female adults are active in fall and on warm winter and spring days.

“A blood-filled female blacklegged tick produces one batch of 2,000-3,000 eggs, then dies. Most ticks don’t survive to the next stage. Most larvae do not successfully feed to become nymphs and many nymphs do not successfully feed to become adults. And many adults do not find a host either,” says Stafford.

Nymphs over-winter in rodent burrows if they fed on chipmunks and white-footed mice, or under leaf-litter if they fell off elsewhere. Ground foraging and ground nesting birds are another preferred food for blacklegged larval ticks.

“A lot of birds readily pick up the ticks when they’re on the ground,” says Stafford. In one study with a bird bander in Old Lyme, CT, he recorded more ticks on birds than on mice caught in the same area. In another study of tick numbers in Westchester County lawns, he estimated that more larval ticks came from robins and other birds than from mice.

Certain birds are “reservoir competent.” They can infect ticks that feed on them, depending on the species of bird and how long they’ve been infected. Birds don’t carry the Lyme disease spirochete Borrelia burgdorferi for life like mice do; they carry it short term. Birds and mice do not get Lyme disease.

“Most of these wild animals get infected but they don’t get the disease. Disease are your symptoms,” Stafford says. “There is a lot of variation in birds’ ability to infect ticks.

Some birds that infect ticks: American robin, Carolina wren, veery, common yellow throat, grackle, house wren. Some birds that cannot infect ticks: gray catbird, wood thrush.

“Deer are infected with the spirochetes and mount a detectable antibody response,” he continues. “However, the deer immune system is good at eliminating the bacteria so that is part of the reason they are disease free, but this is the main reason they are not reservoirs for the spirochete; i.e., they can’t infect the ticks feeding on them. Over 90% of adult ticks feed on deer.”

Since the almost 2 million deer from New Jersey to Maine do not infect ticks, they are just a late night snack with bus service to the nearest tick motel where females drop off to lay eggs. Deer do help increase the number of larval ticks available to feed on small animals.

Studies on islands with high deer densities (>100 deer/square mile) have superabundant tick populations. Islands without deer do not appear to support I. scapularis or B. burgdorferi. (TMH)

Having a fenced property with no deer means short-circuiting the blacklegged tick’s lifecycle. “If you don’t have female ticks coming off deer to lay eggs, you’re just not going to have all those ticks feeding on rodents. You’re going to have, then, no larvae or fewer nymphs and even fewer adults. So the cycles tie in to each other and they’re not mutually exclusive,” says Stafford.

Where the Ticks Are:
Densely wooded areas - 67% of total ticks sampled
Ecotone, unmaintained transitional edge between woodland/brush and lawn - 22%
Ornamental vegetation - 9%
Lawn - 2% (within lawn, 82% are within 3 yards of lawn perimeter)
(TMH)

Some like it hot, but not ticks. They like it moist, protected and shady. They avoid hot, sunny, exposed dry areas like mowed lawns. They prefer woodland, brush, wet leaves, stone walls and groundcover.

“That’s also where you find the most activity for the rodent host or ground nesting birds that ticks feed on,” says Stafford. “There you’ve got habitat and hosts for the tick to do very well. Rodents can move under groundcover without being observed. They don’t like open areas – they’re vulnerable to predators, so they’ll keep to what cover there is. I’ve collected ticks in pachysandra right off people’s doorsteps. Other factors come into play. Some people have pachysandra and have nothing in it if they don’t have many ticks to begin with.”

Studies show that tick numbers on properties within a neighborhood can vary greatly, perhaps because one property is along a deer route and has more ticks coming onto it.

So what’s a gardener to do?
Stafford says home owners need to keep gardens and property as close to a tick-free habitat as possible. The steps to doing so are clear. First, forget the front yard with manicured lawns where most people don’t spend time anyway. Focus on the back, where there is shade, stone walls, shrubbery, brush and where people spend time outdoors.

“There’s where your higher risk is – in the ecotone. In suburbia, there’s a lot of ecotone with deer, mice, chipmunks.”

Stafford’s Recommendations for an Integrated Approach which helps reduce tick, rodent and deer habitat. The fewer deer and rodents, the fewer ticks.

1. Tick-resistant gardens: Think butterfly, cottage, vegetable, herb, colonial style, native wildflower and grass meadows, hardscapes. Surround gardens and intersect with fieldstone, gravel or lawn paths as barriers to ticks.

2. Remove exotic-invasive species: Deer-browse resistant exotic-invasive understory vegetation, particularly Japanese barberry, is associated with greater tick abundance.

3. Companion planting: Surround deer “candy” plants with scented deer-resistant plants such as herbs, mint family plants, ferns and native deer-resistant plants. Not all natives are deer-resistant. Deer-resistant plants may not affect tick numbers unless they’re used enough and strategically placed.

4. Trees and Lawn: Create open, sunny areas. Prune trees to let in more sunlight; keep lawn mowed; remove groundcover around trees.

5. Tick-safe zone around house: Use gravel or mulch near porches and walkways instead of groundcover; use container gardens, xeriscaping; remove leaf litter. Pachysandra and myrtle harbor rodents and ticks.

6. Family and play areas: Isolate from tick habitats. Place swing sets on mulch or gravel. Do not use fast-decomposing mulch.

7. Border fronting ecotone: Create a three-foot mulch or gravel barrier between lawn and brush or stone wall areas.

8. Perimeter spray for ticks: Spray acaricides to control nymphs in May and adults in October. Target perimeter. Done by homeowner or commercially.

9. Biological pesticides:
Some of Stafford’s research involves two naturally-occurring soil fungi used in biological tick pesticides. Tick-ExTM, due on the market in 2011, is non-pathogenic to mammals (including humans) and beneficial insects. The suspension of spores is sprayed to increase numbers of existing spores and also the chances of ticks that will encounter them. The spores attach to the tick’s cuticle, germinate and grow. Tick-ExTM is registered with the EPA and the state. We just have to get the product on the shelf.”

Stafford, with a grant from the CDC, is also working on Nootkatone, a field spray made from essential oil extracts of Alaska yellow cedar, grapefruit and other plants.

“The Nuketone oil does kill ticks,” he says. “It breaks down immediately so you don’t get any residual. With these natural products, the advantage from one perspective is that it’s not going to last in the environment. The disadvantage is it doesn’t last in the environment.” Ticks under leaf litter are not hit with the spray and killed. They emerge active. Stafford and colleagues are trying to develop a little longer lasting formula.

10. Host Management: To exclude white-footed mice & Eastern chipmunks from gardens, use folded hardware cloth (1/4-inch mesh).

11. Host management: To repel deer with a NOFA blessing, use herbal-based deer repellents, ammonia- or hot sauce-based deer repellents. To have an impact on ticks, specific, targeted deer-reduction hunts must reduce the deer population to around 12/sq mi.

In one deer-reduction study in an isolated area in Bridgeport, CT, deer were reduced from over 250 deer/square mile to about 50/sq mi, resulting in > 90% decline in tick abundance. Typical deer densities of towns along the CT shore range from 30 to 60/sq mi. (TMH) Regular hunting does not bring the deer numbers down to that kind of level or anywhere close, Stafford says.

12. Personal Protection
Tick checks and other well-known measures

Says Stafford: “Ticks are essentially mites, have adapted to a blood-feeding lifestyle and they, just like all parasites, take advantage and found a niche that works very well for them.” But by applying Stafford’s concepts of tick-resistant gardens and landscapes, homeowners “can substantially reduce ticks and the risk of Lyme disease.”

Sources:
Interview with Kirby Stafford
Tick Management Handbook: everything you never even thought of knowing, plus X-Rated tick photos.
Center for Disease Control Tick numbers by state

More deer tick info:
An entomologist describes the deer tick life cycle here.
Six labs that test deer ticks here.
These are the accepted Lyme Disease tests here.
Find out about a New Lyme Disease Test here.