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LYME DISEASE’S CONNECTION TO JAPANESE BARBERRY

By Chris Williams on October 16, 2017.

If Japanese barberry is one of your favorite landscaping plants, you should think about finding a new favorite, especially if you worry about Lyme disease. Does that seem like convoluted thinking? What does a garden shrub have to do with a serious disease spread by the bite of a tick?

Tick researchers at the Connecticut Agricultural Experiment Station and UConn discovered a connection between an increased incidence of Lyme disease cases in a region and an increase in the habitat of Berberis thunbergii, a small bush known as Japanese barberry.

WE USED TO LOVE THIS ADAPTABLE SHRUB

The Japanese barberry was introduced to the U.S. in 1875 in Boston and over the following decades gradually became a favorite of landscapers and nurseries. It’s a hardy and thorny shrub that requires little maintenance, has red berries, even comes in various leaf colors. The fact that it is snow, salt, and deer-resistant endeared it to many a Northeastern homeowner.

But beginning in the 1980s, things took an ugly turn. It was noticed that the barberry had leaped the bounds of suburban lawns and was turning up everywhere, displacing native plants in the process. It is now found as far west as Wyoming and has been labeled an invasive pest plant in many states. Since deer will eat everything in woodlands except the thorny shrub, it alone is left to multiply.

TICKS AND MICE STILL LOVE THIS SHRUB

The barberry provides the perfect humid environment that ticks require and which allows them to remain active. The barberry’s dense thorny growth and the accumulated leaf litter below the plant also provides ideal cover for deer mice that are factors in the spread of Lyme disease. The mice pick up infected immature blacklegged (deer) ticks and carry them into other areas.

In a field study to find ticks carrying the Lyme disease organism, the researchers found 120 infected ticks per acre in areas where barberry is not controlled, 40 infected ticks per acre where barberry is contained such as yards, and only 10 infected ticks per acre in areas where Japanese barberry does not grow at all.

Promoting Lyme disease is not Japanese barberry’s only sin. It also crowds out native plants, encourages the development of non-native earthworms that eat the litter layer causing erosion and weed growth, changes soil composition to ward off competing plants, and generally reduces native habitat and biodiversity. In other words, ecologists and forest managers really, really, don’t like Japanese barberry.

Many states and counties, especially in the Northeast, are considering or have already banned the sale, transport, and distribution of Japanese barberry. Agricultural and forestry workers use a propane torch to incinerate invasive barberry shrubs where they stand, but for most of us a chain saw and a shovel can rid our yards of Japanese barberry and perhaps lower everyone’s risk of Lyme disease.

Our Colonial Pest website has dozens of articles on Lyme disease and tick prevention. Just type “Lyme disease” into the search bar at the top of the blog home page.

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