Lyme disease is caused by a tick-transmitted bacterial infection. Most of the ticks that transmit Lyme disease are“deer ticks.” Historically, ticks have proven difficult to control. The complex biologic and ecologic attributes of ticks have made it nearly impossible to significantly reduce any tick population using a single approach.
Fortunately, the incidence of Lyme disease is significantly reduced through vector control. Integrated Tick Management (ITM), a comprehensive program employing environmental and personal protection strategies, is the most effective method in deer tick management. The components of an effective ITM program should be complementary and should avoid having overlapping impact.
The best Integrated Tick Management program includes:
- Monitoring to detect tick infestations and to identify tick habitat.
- Landscape Management to reduce the amount of tick habitat, and isolate it into manageable units.
- Targeted Chemical Control with host- and habitat-targeted insecticide applications.
- Personal Protection by using repellents, protective dress and daily tick checks.
- Behavioral Considerations to modify activities and practices in ways that reduce tick exposure.
Deer ticks progress through four life stages: egg, larva, nymph, and adult. Except for the egg stage, all other stages feed on blood. Ticks typically stay attached to hosts for just a few days in each stage. When they become fully blood-engorged they detach, leaving their host animal.
A vector is an organism that carries things from one place to another. Deer ticks are the main vectors of Lyme disease, serving as the “vehicle” for transmitting a disease-causing germ from one host to another.
Deer ticks obtain their meals from host animals. The type of animal depends on the stage of the tick. Immature ticks will feed on most types of animal (especially small rodents) while the adult stage prefers feeding on larger mammals (especially deer).
The maintenance of tick populations depends upon their host feeding success. To better understand where infected ticks come from we have to subdivide the tick hosts into those that just provide meals and those that also infect feeding ticks with Lyme disease bacteria.
A reservoir is a host animal that both carries and transmits the bacteria to uninfected vectors, continuing the cycle of infection. Small rodents, and in particular white- footed mice, produce 75% of the ticks that are infected with Lyme disease bacteria.
Once deer ticks become infected with Lyme disease bacteria, they transmit the infection by injecting infectious saliva during their next meal. Most larval deer ticks are uninfected when they hatch from eggs. When larvae feed on reservoirs, they may become infected. The bacteria are then carried over as those larvae transform into nymphal ticks. Only after infected nymphs attach to hosts does the bacteria become active in those ticks’ saliva. This activation period takes time, causing a delay of about 24 hours between the time of tick attachment and transmission.
Since deer ticks require high humidity, they seek out habitats that are heavily shaded, damp (but not flooded) and covered with leaf litter. Most immature and adult deer ticks are found in woodlots or the wooded buffers between yards (68 %), and along edge habitats called ecotone, and especially in unmaintained borders. High-risk areas are often found around rock walls, woodpiles and brush piles.
Landscape Management’s role in IPM is to isolate and reduce the amount of suitable tick habitat by:
- Landscaping to manipulate wildlife activity patterns;
- Lowering humidity in the tick’s micro-habitat;
- Pushing back the “danger zone” by edging and mulching borders.
Because ticks (and the risk they present) are only brought onto properties by animals, and they only survive under certain conditions once they are brought in, landscape management presents a real opportunity for tick reduction.
To manage deer ticks through landscape manipulation, the two overriding rules to remember are (1) create an environment that does not attract tick hosts, and (2) make the habitat inhospitable for long-term tick survival.
Basic landscape manipulations include:
- Trimming, pruning, clearing;
- Thinning existing canopies;
- Plant selection;
- Separating “more dangerous” from “less dangerous” areas.
If done correctly, the effect will be to reduce the number of ticks coming onto the property, make the property less supportive of ticks when they are there, and present physical barriers to prevent human exposure to ticks in the remaining tick habitat.
Disrupting Animal Activity
The white tall deer will largely determine the abundance of ticks in an area. (There are more than 13 million white tall deer alone.) But remember, deer only produce uninfected ticks. Mice are to blame for infecting the ticks with Lyme disease bacteria.
One way to discourage deer activity on properties is to landscape with plant material less attractive to deer. Here’s Rutgers’ comprehensive list of plants rated by deer resistance.
Deer Fencing and Repellents
Fencing is another way to reduce or even eliminate deer activity on a property. New fence designs have made fencing a more feasible option than in the past. High tensile angled fences now replace the more unsightly 12′ mesh fencing. A 7-wire electric fence built in a slanted style can effectively reduce deer intrusion even under heavy deer pressure.
Deer repellents may have a place in reducing deer frequency in particular locations. Some deer repellents work by creating an odor obnoxious to deer while others produce an offensive taste when deer eat treated vegetation. Both types have limitations; how much plant material must be eaten before deer get the idea and what is the sphere of influence of odor based repellents. In addition, both types wash off so that repeated applications are necessary.
Discouraging Small Mammals
Any landscape feature or condition that promotes high densities of small rodents (reservoirs) will only increase Lyme disease risk if deer ticks are also present. By thinning vegetative cover and creating “openings” in the upper and lower vegetative canopy, these animals will feel less secure whenever they come out of their burrow sites. They also prefer the security of moving along side of something (foundation, rock wall, fallen tree). Property borders with wooded buffer zones are another problem area. Vegetative buffers also produce the leaf-litter and vegetative cover required by ticks for their survival. To maintain an effective screen, you may want to consider evergreen hedges (pine, spruce or other plants not attractive to deer) that are pruned at the base to give about one foot or so clearance above the ground.
Evaluating plants and plantings for their growth form, their degree of maintenance required, and their attractiveness as deer food, will be the best bet in selecting plants for the tick-managed yard. In considering plants for use in the landscape, it is probably best to choose those that can be pruned away from the ground or those that grow in a more upright manner.
A property is divided into two types of areas when it comes to deer ticks: zones of relative tick safety and tick-dangerous areas. Use edging and mulching wherever possible to demarcate the tick danger areas. Then, whenever family members cross this boundary, they need to remember to check for ticks.
Other Landscape Management Tips
- When mowing lawn edges, direct discharge into shrubbery rather than lawn;
- Clean up old wood storage and junk piles;
- When using power blowers, blow leaf litter and other plant debris out from under shrubs, then rake and remove;
- Position bird feeders away from rodent habitat;
- Keep large beds of weeds or fallow areas mowed.
Host- and habitat-targeted applications of acaricides
Integrated Tick Management attempts to get away from widely broadcast acaricide applications, instead finding alternative means for limiting tick populations in the backyard landscape. Still, to provide the most comprehensive, and most effective prevention against Lyme disease, the careful use of selected acaricide formulations is recommended in most deer tick management programs.
Timing and Rate of Application
In the northeastern and mid-western U.S., it is recommended to apply tick tubes twice per tick season; once in the spring or early summer, when nymphal ticks are actively bloodfeeding on hosts, and once in the late summer, when larvae are active.
The recommended spring application be made between April 1st and June 15th. The summer application is crucial to the success of this tick-control strategy. Mice are more plentiful by late summer and much nest building takes place. In addition, larvae are at their feeding peak during August and it is these larvae that become the next year’s nymphs.
A second application should be made in late June, or at least by early July. Nymphal tick activity (as well as human exposure to nymphs) reaches a peak in late June. And, the effect of the first application will be waning by this time.
In the first year of any tick management program, you may want to add a third application In October or early November (preferably after a frost or two) to hit adult ticks questing on brushy vegetation. Ideally, you want to spray after leaves have dropped from bushes so that questing adult ticks will be exposed.