Create an Environmentally-Friendly Yard that Discourages Ticks

As someone who was diagnosed with Lyme Disease three times between September 2010 and January 2017, I've become very interested in learning how to avoid contact with ticks without the use of toxic chemicals. I love the outdoors, we have four dogs, and Tom's work in lawn care and landscape maintenance makes us all an easy target for the nasty little bugs. Pennsylvania has a large tick population and is one of the states with the highest incidence of ticks and tick-borne illnesses. There were just under 13,000 reported cases of Lyme disease in Pennsylvania during 2016, and 2017 was expected to be the worst year ever for deer ticks in Pennsylvania. The report isn't in yet.

The increase in ticks is due to several factors. There was a bumper crop of red oak acorns during the fall of 2016, and the winter of 2016/2017 was warmer-than-usual overall, resulting in a population explosion of white-footed mice, which typically provide deer tick larvae with their first blood meal.

Although April through October is considered tick season, Lyme disease is a year-round problem. I thought that we didn't need to worry about ticks in the winter until we found ticks on the dogs and I had one on me in mid-January.  A few weeks later I was diagnosed with Lyme disease for the third time. The weather in January was a rollercoaster with the temperature ranging from the low teens to the upper 60s. During my visit with my infectious disease physician, I learned then that ticks are active and will feed any time the temperature rises above 32º F. Winter does not provide a reprieve from exposure to ticks and tick-borne illnesses. They must have come from our yard. The dogs and I had not been on any walks in the woods. We live in town and don't have deer anywhere near our property, although our yard is full of rabbits, squirrels, birds, and the occasional skunk. This got me thinking about how ticks carrying Lyme were getting into our yard and what we can do to limit our exposure to them, preferably without using toxic chemicals. What modifications can we make to our yard to restrict ticks and the animals, such as deer, white-footed mice, and birds, that serve as their primary hosts?

A Tick's Life-cycle

It's helpful to understand the life-cycle of deer ticks, also known as black-legged ticks (I. scapularis). These ticks have a two- to three-year life cycle, which consists of three-stages: Larvae, nymphs, and adults. They spend the majority of their lives in the environment either seeking a host, molting or merely passing through an inhospitable season (e.g., hot summers or cold winters). They only feed on hosts three times during their lifetime. Larvae which hatch from eggs between May and September are the size of a period at the end of a sentence. Initially, larvae do not carry diseases. At this stage larvae will consume their first meal from a diseased host, usually white-footed mice, other small mammals, or birds. If the host animal is infected with disease-causing organisms, the larva will become infected and be able to transmit these microorganisms during future feedings. Tick larvae that feed on uninfected hosts will not be able to transfer disease in later feedings. Once the first meal is complete, larvae molt into nymphs and become dormant until the following spring.

During the next spring and summer, usually May through early July, nymphs, which are about the size of a pinhead, become active and find a host animal for their second feeding. Nymphs that were infected during their first feeding as larvae (10-36%) transmit Lyme during this second feeding. Nymphs that weren't infected during their first feeding cannot transfer the disease during their second meal, but they can become infected if the host animal is infected. Most Lyme disease cases are associated with this second feeding during this nymphal stage. Nymphs molt into adult female and male ticks in the fall.

During the third stage, the female adults feed, over the course of several days, on white-tailed deer and other large mammals, until they become engorged with blood. During this last feeding, they can transmit Lyme if they were infected during the earlier two stages. If they weren't infected, they would not acquire the disease during this last feeding as adults. They mate, lay eggs, and die. If they don't feed in the fall, they will try to find a large mammal host in the following spring. Male deer ticks, on the other hand, attach to a host to wait for females but do not take a blood meal. Since they don't feed, male ticks don't spread the disease during their adult stage.

Deer ticks are primarily found in densely wooded areas (67% of total sampled) and the unmaintained transitional edge habitat between woodlands and open areas (22%). They prefer a dark, humid environment over areas that are dry and sunlit. Fewer ticks are found in ornamental vegetation (9%) and lawn (2%). Most ticks (82%) are located within 3 yards of the lawn perimeter particularly along woodlands, stonewalls, or ornamental plantings. In a study of tick egg-laying, female ticks from deer were found to survive in field bedding areas and lay eggs from which larvae successfully hatched. However, larval survival in the field was shorter than in the woods, and they are less likely to be picked up by a mouse host.The majority (about 75%) of Lyme disease cases are associated with outdoor activities around the home. Ticks don't jump, fly, or drop from trees. They grab onto passing hosts from leaves, tips of grass, and bushes, usually starting around the ankles and traveling upwards until they find a place to feed.

Create tick-free zones in your yard

Removing plants that attract deer and constructing physical barriers may help discourage deer from entering your yard and bringing back-legged ticks with them. Food and shelter are essential requisites for wildlife. The residential landscape can be particularly attractive to white-tailed deer and conducive to mice, both important hosts in the prevalence of ticks and Lyme disease. One component of a tick management strategy is managing deer and small rodent activity in your yard. The Connecticut Tick Management Handbook provides valuable advice for keeping deer ticks out of your yard. Tick abundance is related to landscape features that provide a suitable environment for the tick and its animal hosts, particularly white-tailed deer, and white-footed mice.

While there is a lot of variation in tick numbers between homes, larger properties are more likely to harbor ticks because they are more likely to have woodlots. Tick abundance in manicured lawns is also influenced by the amount of canopy vegetation and shade. Groundcover vegetation can harbor ticks. Ticks are commonly found in the grass and bushes adjacent to Woodland paths.

“Tickscape” practices, which can reduce but not necessarily eliminate ticks, should be incorporated into landscape design and maintenance and general lawn care in Lyme disease-endemic areas. Fewer ticks have been found on well-maintained lawns, except on areas adjacent to woodlands, stonewalls, or heavy groundcover and ornamental vegetation. Clearing leaf litter and woodchip barriers have been documented to help reduce ticks on the lawn. The purpose of implementing a tick management program is to discourage activity of several key tick hosts and create a physical and/or chemical barrier between woodland habitat and areas the family uses most frequently. The lawn perimeter, brushy areas and groundcover vegetation, and most importantly, the woods, form the high-risk tick zone.

The idea for residential tick management is to create a tick managed area around your home that encompasses the portions of the yard that your family uses most frequently. This includes walkways, areas used for recreation, play, eating or entertainment, the mailbox, storage areas and gardens. Altering the landscape to increase sunlight and lower humidity may render an area less hospitable to ticks. Management of the habitat should focus on the areas frequently used by the family, not necessarily the entire property.  Open up to direct solar exposure the part of the landscape used or frequently traveled by family members to reduce tick and small mammal habitat and cover. Bright, sunny areas are less likely to harbor ticks. Xeriscaping, which uses creative landscaping to conserve water, helps isolate frequently used areas, such as pool areas, decks and patios, playgrounds and sandboxes, and paths.  Xeriscaped areas can provide an attractive focal area that requires little maintenance and reduces the need for water, fertilizer, and chemicals. Landscape materials such as laid brick, wood decking, stone paving, raked gravel or pea gravel (set down slightly from bordering bricks, stone, or paved areas), and concrete can be used to create a patio and paths. Gravel can be laid over a layer of crushed stone covered with black plastic to discourage weed growth. Some plantings can be in raised beds or containers. Xeriscaping can also be used to create a barrier between areas frequented by family and surrounding woods to help reduce tick habitat and isolate parts of the yard from tick hot spots, such as woods, dense vegetation, groundcover, and stonewalls. Regular lawn care and landscape maintenance are important. Properly maintained each year, the barrier may allow fewer ticks to migrate from the woodlands into the lawn. It also serves as a reminder that people who cross the barrier may be at higher risk of getting ticks. The application of a barrier or buffer will be easiest where there is a sharp delineation between the woods and lawn. The grass needs to be kept mowed. Leaf litter, brush, and weeds should be regularly cleaned up and raked or blown out from under shrubs and bushes. Composting or removal by appropriate bagging is an acceptable method of disposing of leaf litter. Leaves should not be simply moved to another part of the property. Stone walls, wood piles, and bird feeders must be kept neat and clean to discourage rodent activity. Stonewalls and small openings around sheds and the home need to be kept clean and sealed. Trimming tree branches and shrubs allow more sunlight in the yard and reduce dark, humid areas that attract ticks. The use of groundcover should be limited to areas that aren't frequented by people and pets because it provides a dark, humid environment that attracts ticks and gives rodents a place to hide. While groundcovers should be avoided, mulch, which is used to suppress weeds and help retain soil moisture, can help reduce tick movement. In the laboratory, untreated landscape stones, pine bark, and woodchips have been shown to deter tick movement. A barrier that is at least three feet wide may help reduce tick abundance on the lawn, although results have been found to vary widely from home to home and from year to year depending upon other factors (i.e., the density of woods, amount of shade, initial tick densities).
Butterfly gardens, vegetable gardens, formal herb gardens, colonial style gardens, wildflower meadows and hardscapes can be used as environmentally-friendly alternatives for homeowners who aren't interested in large lawn areas. Eliminating woodland areas and other wildlife habitats are not recommended because biodiversity is essential. Evidence suggests that the critical factor is the reduction or elimination of mice and deer on the property. In general, ornamental grasses and ferns are deer resistant and may be suitable choices in sunny and moist shady areas, respectively. A number of medicinal herb varieties, ornamental herbs, and butterfly garden plants are deer resistant. The most deer resistant plantings should be placed at the edges and entrances of the property and the most browse susceptible plants closer to the house or areas frequented by people and pets. Sensitive plants can be surrounded by less palatable species. Clean up fruits and other produce from under trees or crop plants. While eliminating cover like mixed tall grass and brush may help discourage deer from bedding near the home, deer will bed wherever they consider it safe – even open lawn.

Discourage deer

White-tailed Deer

Deer Fencing is the most effective method to control access by deer to a property. Fences can keep deer from large garden beds or small to moderate sized home lots.  Fencing of smaller areas also may be beneficial, but tick management practices within the enclosure and the use of an insecticide at the fence perimeter may also be needed. A deer fence does not stop small animal movement and tick movement. Barrier fencing can be used to protect individual trees, shrubs or other plantings from deer. There are many types of deer fences and selection will depend upon deer pressure, area to be protected, and site characteristics. It's also important to check into local restrictions or ordinances that many communities have on the type and height of fencing allowed before purchasing fencing. The most common choice in a fence is a plastic or wire mesh vertical fence. An electric fence is another option. An electric fence requires maintenance, proper grounding, and may not be appropriate in many residential settings. A vertical or slant seven-strand, high-tensile electric fence is very useful for larger areas where deer densities are high. The exclusion of deer from areas of 15 to 18 acres with a slant high-tensile electric fence was shown to reduce the abundance of black-legged tick nymphs by as much as 84% and larval ticks by 100% approximately 70 yards or greater inside the fence. A number of companies specialize in providing deer fencing and can provide the fencing materials or install the fence. Non-electric fences may be vertical or three-dimensional. A vertical fence requires the least space and a wide variety of fence materials and designs are available. Increasingly, a black polypropylene plastic fence-like mesh or steel mesh is being used instead of a chain-link for vertical fences because of reduced cost, low maintenance, long life, and near invisibility, an attractive feature in the residential landscape. The plastic material comes in rolls of various lengths and 7.5 feet wide and can be fastened to existing trees or several different types of posts. While deer can jump a vertical fence of eight feet from a standing position, they rarely do so and are more likely to try and push under fencing. Proper anchoring or staking of the fence along the ground is essential. Single or multiple electric strands also can be placed along the top of a vertical wire or mesh fence. Another option is a slant deer fence set at an angle of 45 degrees use in areas with moderate to high deer densities, but it requires more space (about 6 feet of horizontal space). Deer cannot clear both the height and width of the fence and often find themselves under the top outer wire. Solid 5- to 6-foot fences are also useful. Access gates, driveway gates, or in ground driveway deer grates (similar to cattle guards) will be needed to completely enclose the area an allow owner and vehicle access. Deer Repellents: The use of deer repellents may reduce damage to plants and help defer the animals elsewhere, but by itself will not impact tick abundance unless deer consistently avoid the property entirely. Repellent performance is highly variable depending upon the product (most are either odor or taste-based), rain, the frequency of application, and the availability of other food sources for deer. Nevertheless, some repellents are relatively effective with low to moderate deer densities.
Deer Resistant Plantings: Substituting less palatable landscape plants may discourage browsing around the home, reduce damage to ornamental plants and may help make the yard less attractive to deer, though deer will also readily graze on lawns. The use of deer resistant plantings may have no impact on ticks unless deer consistently avoid the property and the explicit use of these plants as part of tick management has not been examined. It merely seems to make sense to make your yard and plantings less attractive to deer. No plant is completely deer resistant, and susceptibility depends upon deer density, food availability, and food preferences, which can vary regionally. Plant selection depends partly upon the type of terrain you have: Is it
 A sunny, moist yard?  A dry, sunny garden? A dry, shady garden?
A wet, shady yard Or, close to streams or ponds?

It also depends on the effect that you desire -- is your goal fragrance, foliage color, seasonal color, showy borders, etc.?

Use of native shrubs and trees is encouraged, and the use of invasive plantings is discouraged. Some non-native invasive plants, such as Japanese barberry, multiflora rose, Asiatic bittersweet, and several non-native honeysuckles, which are very resistant to deer browse damage, can crowd out natives.

A rating of deer browse damage to many plants was compiled at the Connecticut Agricultural Experiment Station (CAES) from a survey of Connecticut gardeners. A comprehensive list of the survey results with plants ranging from very susceptible to highly resistant to browse damage is available in CAES Station Bulletin 968. Information is also available on deer resistant plantings and deer proofing from a variety of books and handouts. Many nurseries and garden centers can provide a suggested list of deer-resistant plantings.

Consider using a chemical control agent

A single springtime application of acaricide can reduce the population of ticks that cause Lyme disease by 68–100%. A pesticide application can be focused on the landscape barrier or buffer zone to increase the effectiveness of the barrier.       
Integrated pest management (IPM) basically involves the selection and use of several methods to reduce, rather than eliminate, a pest population with expected ecological, economic, and sociological costs and benefits. For ticks, this may involve the use of landscape practices to reduce tick and host animal habitat adjacent to the home, management or treatment of host animals, targeted applications of least-toxic pesticides to high-risk tick habitat – all in conjunction with tick checks and other personal protective measures to either reduce the number of infected ticks and number of tick bites. The ultimate goal, of course, is to reduce the number of human cases of disease as much as possible with the resources available. A decision has to be made on how much one is willing to spend and what ecological impact one is willing to tolerate to reduce the risk of a tick-borne illness. An integrated management approach does not necessarily preclude the use of pesticides, for example, but seeks to use chemicals effectively and responsibly in order to minimize and reduce exposure and use. Research and computer models have shown that pesticides are the most effective way to reduce ticks, particularly when combined with landscaping changes that decrease tick habitat in often-used areas of your yard.

Tick Distribution and Creating a Tick Safe Zone in the Residential Landscape

Small Mammals and Birds Rodents and birds can transport ticks onto your property. The importance of these animals in the dynamics of Lyme disease depends on the abundance of the animal host, the number of ticks feeding on the host, and the host’s ability to infect feeding ticks with the Lyme disease. Some animals may have a lot of ticks, but not be able to infect them. White-footed mice, Peromyscus leucopus, are generally the most abundant and efficient animal reservoir for the Lyme disease bacteria. They contribute more infected ticks than eastern chipmunks or meadow voles. White-footed mice also are a reservoir for the causal agents of ehrlichiosis and babesiosis. Over 90% of white-footed mice will be infected with Lyme in many areas and up to half have been found to carry all three pathogens in some areas. In one study, a single mouse was estimated to infect as many ticks as 12 chipmunks or 221 voles. By contrast, squirrels have a lower likelihood of hosting Lyme infected ticks. One study indicated that squirrels might reduce or dilute the number of infected ticks in the landscape. This possibility is encouraging since our next door neighbors feed the squirrels and my last exposure to Lyme disease had to be connected to our backyard since we hadn't been anywhere else. Birds are frequent hosts for immature stages of the black-legged tick. At a woodland residence, 26% of birds were infested with ticks, and 94% were black-legged ticks. While some bird species such as the American robin, Veery, Grackle, Common Yellowthroat, Carolina Wren and House Wren, can infect feeding ticks with Lyme, other species such as the gray catbird and wood thrush do not. Due to variability in bird species composition, population, habitat preferences, hosting competence and feeder activity, it is unclear how many ticks, much less those infected with Lyme, most birds actually contribute to a typical residential landscape. One early study found that American robins, a reservoir competent bird, were likely contributors to the nymphal tick population found in some suburban residential landscapes. Unlike mice, however, reservoir competency in robins declines after 2 months. A recent study suggested most birds probably contribute few infected ticks and may actually dilute pathogen transmission, at least in comparison to mice. Bird feeders in landscaped areas like mowed lawns were not found to be a risk factor for Lyme disease, probably because the habitat does not favor tick survival and seed feeding birds that frequent feeders in the summer do not deposit many ticks. However, higher tick abundance has been noted where feeders were installed at or beyond the lawn edge in wooded habitat suitable for tick survival and rodent activity (Gary Maupin, CDC retired, personal observation). Adult ticks, which are active in the fall, winter and spring months, do not feed on birds. It is unknown what impact summer or winter fruit-bearing trees and shrubs for birds has on the prevalence of ticks as related to mouse and chipmunk activity, as seeds and fruits can also serve as a food source for these animals. Many berry plants, however, are important to fall migrants and the berries are quickly consumed. Deer resistant bird favorites include bayberry (Myrica pensylvanica) and Virginia creeper (Parthenocissus) and highbush blueberry (Vaccinium corymbosum – produces summer berries); cedars and certain holly cultivars, however, are subject to heavy deer browsing. Common Winterberry is also fairly susceptible to heavy deer browse damage. It requires both female and male plants to produce winterberries for birds. Native viburnums will suffer only occasional to minimal damage from deer and are good bird plants. Japanese barberry is considered invasive. Possible small animal and bird management strategies include: • Keep potential mouse nesting sites in stonewalls and woodpiles near the residence free of brush, high grass, weeds, and leaf litter. • Seal or rework stonewalls near or under the home to reduce harborage. • Move firewood away from the house. • Place the birdhouses and feeders away from the house, but it is unknown if this will decrease risk of exposure to ticks. Clean up spilled feed (spilled bird feed can also attract mice). • Set up bird feeders in late fall and winter when natural foods are scarce (and the immature stages of I. scapularis are not present on birds). • Seal foundations. For example, a garden shed on cement blocks can harbor raccoons, skunks, or woodchucks. This can be avoided through a proper foundation or use of hardware cloth buried at least two feet beneath the ground. A poorly sealed building or old garden shed can harbor mice. Tick IPM practices are covered under pest and wildlife management guidelines. Practices that are preferred to manage ticks would include personal protection measures, making the environment unsuitable for the pest (i.e., landscape modifications), deer resistant plantings (natives recommended), fencing against deer, and herbal-based deer repellents. The use of arthropod pathogens like entomopathogenic fungi (fungi that kill insects), diatomaceous earth, insecticidal soaps and botanical insecticides are allowed under the standards. However, botanicals cannot be formulated with aromatic petroleum distillates. Ammonia or hot sauce based deer repellents are allowed. Prohibited under the organic standards are all synthetic insecticides and piperonyl butoxide as an insecticide synergist, rodenticides containing warfarin, predator urine (due to collection practices), and products containing sewage sludge (e.g., Milorganite). Biological Control of Ticks Ticks have relatively few natural enemies, but the use of predators, parasites, and pathogens has been examined for tick control. Tick predation is difficult to document and observations are sporadic. Most arthropod predators are non-specific, opportunistic feeders and probably have little impact on ticks. Anecdotal reports suggested that guinea-fowl or chickens may consume ticks and impact local tick abundance. However, there is no good evidence to support this and turkey foraging was not found to reduce the local density of adult ticks. A minute parasitic wasp, Ixodiphagus hookeri, parasitizes blacklegged ticks in a few areas of New England with superabundant deer and tick populations. However, studies indicate that the usefulness of this wasp to control black-legged ticks is very limited. Insect parasitic nematodes have been studied as possible biological control agents. Engorged female black-legged ticks are susceptible to certain types of nematodes, but these nematodes are too sensitive to the colder autumn temperatures when the ticks are present. The application of entomopathogenic fungi, however, is a promising approach for controlling ticks. Several fungi have been shown pathogenic to black-legged ticks. A perimeter treatment of existing commercial formulations of the fungus Beauveria bassiana and with Metarhizium anisopliae at residential sites has been shown to control I. scapularis in small experimental trials. The EPA has approved M. anisopliae for residential outdoor grub and tick control (Tick-Ex, an oil formulation, and Taenure, a granular formulation; Earth BioSciences, Glastonbury, CT). At the time of this writing, additional trials and commercial development are in progress. Entomopathogenic fungi, applied like a traditional pesticide, may be an option in tick management programs, and an oil-free formulation could meet organic standards. Ticks cannot fly or jump; they must make direct contact with a host. Once on a host, a tick may attach quickly or wander over the host for some time. Blacklegged ticks, or deer ticks, feed on a wide variety of mammals and birds, requiring 3 - 7 days to ingest blood, depending on the stage of the tick.

Reduce Ticks in Your Yard

Botanical and Other Repellents With increased environmental awareness, the focus for some residents has been to provide a more natural or organic landscape, with reduced inputs of energy, water, pesticides, fertilizer, and labor, and provide increased wildlife habitat. Some shrubs and other plants are selected for their wildlife value due to the berries, fruit, and cover they provide for birds and small mammals. Many resources are available to help create backyard wildlife habitats. How can the desire to have a more natural, environmentally friendly habitat be balanced with the need to reduce contact with animals carrying ticks and the creation of a tick-safe zone? The presence of deer and rodents will result in the presence of ticks. Little information is available on how to integrate these two different objectives. Open lawns harbor fewer ticks and wildlife that carry potentially infected ticks. There is some evidence that increased animal diversity can actually reduce the rate of transmission of tick-associated disease, resulting in fewer infected ticks, although ticks are still present. The fragmented woodland and ecotone environment of suburbia favors the deer, mice, and chipmunks most involved in the maintenance and transmission of ticks and tick-associated diseases. Mixed ecotone with uncut grass, wildflower and shrubby vegetation, especially adjacent to woodlands is good deer, mouse and tick habitat. Little is known about relative tick densities in various alternative landscapes to turf like wildflower meadows, gardens, and butterfly gardens. It is not known what specific plants or plant groupings may be associated with more or fewer ticks or if it makes that much of a difference. Some plants used in butterfly gardens are attractive to deer, while most herbs are highly resistant to deer browsing. Fencing against deer will allow greater landscape flexibility. While data is limited, meadows appear to harbor few black-legged ticks except along the edge with woodlands, dense vegetation and stonewall. If a property is large enough, a separate wildlife and tick managed zone could possibly be maintained.   "New research finds 1 in 5 deer ticks carry Lyme disease in the Lehigh Valley," The Morning Call by Sam Kennedy (Oct 15, 2016). CDC Features: Stop Ticks