Japanese Barberry and ticks

Japanese barberry (Berberis thunbergii) is a very popular ornamental and it is widely planted throughout our neighborhood landscapes. A reason for its widespread use is that barberry is very hearty, has colorful foliage and produces attractive, bright red berries that many birds eat. Despite its widespread use, barberry has become a very serious invasive plant in many of our forests.

Credit: frederick.forestryboard.org - Mike Kay

Barberry can grow on most sites and thrives in open and shady conditions. This prolific plant produces red fruits that develop in the fall and remain on the plant throughout the winter. Barberry seeds are eaten and dispersed by birds. Once the barberry becomes established, it can also spread through underground rhizomes and by sending out shoots (layering). Due to its aggressive dispersal and dense form, this plant can overtake native vegetation. Deer do not favor this spiny plant and tend to leave it alone, which also aids its establishment. This spiny plant can grow to a height of nearly 10 feet and make it difficult and painful to walk through dense stands.

Not only does barberry choke out native vegetation, it also promotes the establishment of nonnative earth worms that quickly decompose organic leaf matter and other material resulting in increased runoff, soil compaction, erosion, decreased soil fertility, and resultant sedimentation in our streams and waterways. If these issues weren’t enough, many recent scientific studies now link the presence of barberry with increased tick populations and heightened risk of Lyme disease. Tick populations and activity levels increase in warm and humid environments.

Dense stands of barberry provide an almost constant 80 percent relative humidity level and provide the ticks with a launch pad to jump onto an unsuspecting host. Studies also link increased white-footed mice populations (a vector of Lyme disease) with barberry stands. Studies made by the Connecticut Agricultural and Experiment Station suggest that forests that contain barberry thickets have 67 percent more ticks than forests that do not contain this invasive species. The study also concluded that if you eradicate barberry from a forest, the amount of Lyme infected ticks drops from 120 per acre to 12 per acre, an 80 percent decline. Many ecologists correlate the historical dispersal of barberry throughout our forests with the spread of Lyme disease to these areas; indeed, if you look at maps of barberry ranges and Lyme disease cases they nearly overlap.

When nonnative species are introduced into a new ecosystem they often experience uncontrolled spread, impacting the local plant and animal populations. In the case of barberry, the unfettered spread not only hurts local plant communities but it is being linked to a serious public health issue. Scientific studies are concluding that increased barberry colonization is causing an increase in tick populations and an increase in Lyme disease. These studies also conclude that controlling barberry stands decrease both the incidence of ticks and Lyme disease.

Article by FCFCDB

Nature Notes for 9/22/2013