Garden Report: Japanese Barberry and ticks

Sun, 05/28/2017 - 7:00am
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What’s not to love about a drought- and deer-tolerant ornamental shrub with colorful foliage, plentiful red berries and cute, although inconspicuous little flowers? Quite a bit, it seems.

Japanese barberry (Berberis thunbergii) was brought to the United States in the late 1800s. Fast forward 125 years and it has been classified as invasive in 31 states, including here in Rhode Island. It can be found in many areas on Block Island, in yards, along roads and in the woods. Unfortunately, it is also easily found at nurseries and from major online plant retailers. 

Barberry is distinctive and easy to recognize by its usually purplish foliage (sometimes it’s more green) and small, elongated red berries. Its thorns protect it from the deer and small animals find it provides a safe place from predators. Birds eat the plentiful berries and then spread the undigested seeds. 

Back in 2011 researchers from the University of Connecticut’s Department of Natural Resources began studying it in woods that had grown up from abandoned farm fields. What they found was quite interesting. Assistant Extension Professor Tom Worthley, along with fellow professor Scott Williams, and Jeffrey Ward, from the Department of Forestry and Horticulture at the Connecticut Agricultural Experiment Station in New Haven were studying the problems brought about by barberry – and they found a few.

First, barberry alters the chemistry of the soil around itself, attracting another invasive – this time the earthworm – which chews up the leaf litter on the ground, leaving it bare and susceptible to erosion. 

Even worse, it provides the perfect environment for disease carrying ticks to thrive in. The dense foliage creates a pocket of high humidity underneath, allowing the ticks to remain active for more hours of the day than they normally would be. 

In an article from 2012 in UConn Today, Williams is quoted as saying: “When we measure the presence of ticks carrying the Lyme spirochete (Borrelia burgdorferi) we find 120 infected ticks where barberry is not contained, 40 ticks per acre where barberry is contained, and only 10 infected ticks where there is no barberry.”

And here’s where you double your trouble. Not only do the ticks find the barberry hospitable, so do mice, which have been found to be just as much, if not more, of a vector in spreading Lyme disease as deer, although the mice carry the ticks in their nymphal stage as opposed to the deer, which carry the ticks in their adult stage.

The UConn Today article goes on to say: “And although the prevalence of B. burgdorferi infection in adult ticks is twice that found in nymphs, it is estimated that nymphs are responsible for 90 percent of human disease transmission. This is due to their abundance, and because they feed in the summer when people are most apt to be involved in outdoor activities.”

When researchers explore methods of eradicating an invasive plant, they usually do so in various different ways. For the thorny barberry, it is recommended that larger plants be cut back to one inch stubs. Then the plant can be pulled, if it’s not too big, or dug up. It’s important to remove the crown of the plant, which is where the stems meet the root system. 

Some sources recommend using glycosphate, the active ingredient in Roundup, in killing the stubs. Instead of spraying the chemical, it is painted onto the just-cut surface of the stub. While this method may mitigate the potentially harmful (“probably carcinogenic”) effects of the chemical, it should only be used as a last resort, and I wouldn’t recommend it myself.

The trio from UConn found that burning the plant around the base can be the most effective. Native New England forest plants are used to fire periodically, but not so the Japanese barberry. In the 2012 article, they recommended the use of a propane blowtorch to burn the shrub, cautioning that of course it should only be done when conditions are wet. 

Later articles, easily found online, suggest that the burning might need to be repeated to be effective. I originally wrote: “Burning is best done with a hose and perhaps a firefighter on hand. At least warn the fire department in advance if you wish to conduct a burn.” But then I asked Fire Captain Joe Sprague if this was the proper procedure, and was told that any “open burning” in Rhode Island was illegal under state law.

Oh, well. With all the other invasive plants popping up in my yard, the two barberry bushes are the least of my problems. So far I have only made verbal threats against them.   

As the gardening season begins, consider tearing out your barberries and making way for a native shrub, such as the bearberry. It too has lots of red berries that are good for birds, it’s deer resistant, and good for the local pollinators. And as opposed to being harmful to your health by abetting those pesky ticks and mice, it has some medicinal qualities. There’s lots of love there.