The Surprising Relationship Between Lyme Disease and Japanese Barberry

There is a multi-year study going on now in Connecticut which looks at the relationship between Japanese barberry (Berberis thunbergii), white-footed mice and blacklegged ticks.  Admittedly a strange combination. 

Recently, results of the first two years of the study were released and they are a bit surprising.  In essence, the study found the larger the number of Japanese barberry in an area, the higher the incidence of Lyme disease carrying ticks.  Yikes!  Yet another reason to rip these invasive plants out of your garden.

 Here are a few highlights from the study:

  – The study’s authors asked two basic questions. First, do higher populations of white-footed mice and blacklegged ticks protected by a dense under story of Japanese barberry have a higher incidence of Lyme disease? And second, if Japanese barberry are controlled, will the population of blacklegged ticks be reduced and therefore, the rate of Lyme disease infection in white-footed mice also be reduced?

- Japanese barberry was chosen, in part, because it is generally considered a deer-resistant shrub in most locations.  For anyone who gardens in an area with deer, you know how fickle a deer’s taste buds can be but Japanese barberry is typically uneaten.

- The study looked at three test sites in Connecticut.   The first site was located in area where the Japanese barberry was very dense. The second site included a thick grove of Japanese barberry that was cut to the ground and controlled during the study.  The third site contained no Japanese barberry at all.

- Results of the first two years of the study have shown that feeding larval ticks and adult tick populations were highest in the high density barberry site.  The highest incidence of Lyme disease carrying ticks was also found in the high density barberry areas. 

- After cutting the Japanese barberry, the infection rate of Lyme disease in the white-footed mice remained the same the first year but was significantly reduced the second year , becoming equal to the areas that had no Japanese barberry growing.

- The study concluded that Japanese barberry infestations threaten humans by creating a favorable environment for ticks and mice.  And high populations of mice and ticks leads to an increase in the incidence of Lyme disease.

All in all, the study gives gardeners yet another reason to stop buying and planting Japanese barberry.  Unfortunately I was not able to find a free link to the full study but I do have a .pdf copy that I will be happy to share.  If you’d like a copy of the study, just leave a comment and I’ll contact you directly.

46 thoughts on “The Surprising Relationship Between Lyme Disease and Japanese Barberry

  1. Debbie, I’m definitely interested in reading this study and learning what journal it was published in.

    My personal experience backs up the findings … I do not have a heavy barberry population in the woods surrounding my house, and any that do sprout up I quickly pull and burn. At the other end of my street, however, there are thick stands of barberry throughout the woods. My neighbors living near the barberry infested areas have lots of ticks; we have very few.

    Thanks for sharing this extremely valuable information, and Happy New Year.

    • Joene,

      Happy New Year to you too. Thats’s interesting that you have found the same evidence as the study. I just e-mailed you a copy of the study, I’m sure you’ll find it interesting reading.

  2. Hmmm. They should have included a site with dense shrubbery but not Japanese barberry. Otherwise, how do we know it was barberry specifically that was good tick habitat? Maybe any kind of shrubbery would do the same thing.

  3. Fern,

    That’s a good question. Japanese Barbery (JB) was chosen because it is the dominate understory shrub now found in CT forests. Several factors, including the invasive habits of JB and the fact that deer have browsed to death many of the other understory shrubs, unfortunately means JB is basically all that’s left in the understory of many of our forests here in CT.

    JB has also been found to be an ideal ‘questing habitat’ for blacklegged ticks. And other studies (cited in this study) have shown there are more ticks in forests with dense JB than in nearby forests without JB.

    Since this study was looking at the relationship between ticks, mice, deer and Lyme disease and how Lyme disease can be reduced, it simply makes sense to test in an area where the conditions are prime for tick survival.

    If you’d like a copy ofthe study so you can read it, just let me know and I’ll e-mail it to you.

  4. This is fascinating, Debbie. I’m going to go post this on twitter now. I hate Barberry because of all the darned thorns, but this gives me yet another reason to avoid them.

    • Gen,

      Thanks for helping to get the word out. I’m not sure how prevelant Lyme Disease is out near you but here in CT, it’s a major issue. In my mind, any small steps that we can take to limit our exposure to ticks is worth knowing about. I agree with you about barberry and I always find it frustrating when a client wants to use barberry in their garden, despite my best efforts to sway them to use a more suitable alternative. While the leaves of some cultivars are interesting, the negatives far outweigh the benefits of their color, at least in my mind.

    • Hi, I really enjoyed your post, and I would love to read the study too! I find it so interesting that this invasive plant Japanese Barberry may be housing a perfect environment for Lyme ticks, and yet another invasive plant Japanese Knot weed is used to help treat Lyme! Nature’s tricks… and gifts…

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  11. Omitted is the comparison to density of the non-barberry hedgerow. The density and not the species could explain the higher incidence of ticks/mice, etc. Do you have information that describes the density of the non-barberry hedgerow?

    Without this, the study doesn’t make sense. There is a large difference between a hedgerow that is dense and mostly barberry, close to the ground , etc. and the natural hedgerow that is mixed in a wooded area that is not as dense.

    Thanks! Abigail.

    • Hi Abigail,

      The study did not look at Japanese barberry (JB) hedgerows or any type of hedgerow for that matter. The study looked at JB growing primarily as understory shrubs in CT forests. The density of the JB in two of the sites did vary and was compared to a JB-free site. If you’d like a copy of the study, please let me know and I’ll be happy to forward a copy to you.

      Thanks for stopping by and leaving a comment.

  12. Fab! When I have more time I will peruse your blog site! This caught my attention b’c a friend of mine is writing an article about the relationship for a science journal and I, as a professional horticulturist, have my own somewhat rebellious point of view about it, and am completely interested.

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  14. five cases of lyme disease in my immediate family within in the last few years.
    the stands of japanese knotweed here are formidable and I am sure are crawling with deer ticks……been trying to kill the stuff with earthmoving machinery, mowing, and herbicides north Butler County . western Pa. is
    getting badly infected. for thirty years I never had a tick on me, and I lived in the woods. last few years it became a daily risk.
    tom rehm.

    • Tom, I can relate to what you’re going through. We’ve been finding ticks more frequently this year too. As Lyme disease becomes a problem in many parts of the country, it can be maddening to try and figure out how to deal with the increase in ticks and still be able to enjoy your garden. Good luck removing your knotweed, that’s a massive undertaking.

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    • Hi Tom, I don’t really know but I would assume so, based purely on the fact common barberry has the same thorny branches that presumably are a primary factor with Japanese barberry. Wish I could be of more help.

  16. Hi,
    Our little community is on the verge of a deer cull to minimize the threat of lyme disease. Could you send me a copy of the report showing the relationship between barberry, mice and ticks?

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  18. Just wondering if there’s anything new on this. Heard a piece on Faith Middleton’s show today regarding the relationship. I’m a complete novice in Litchfield County, wondering how prevalent the Japanese Bayberry species around here and what else I may need to know.

    • To tell you the truth, I haven’t really heard any updates but you could probably check out the UCONN website for any research updates. I think Japanese barberry is quite prevalent throughout the state although it does seem like some areas have a bigger issue than others.

  19. I’ve got some news for you-there’s not a Japanese Barberry in sight-but lots and lots of ticks! (At least one a day on me alone, 21 off my dog in one day!)
    I am in the middle of the woods, with meadow, understory and tall trees…and ticks and bugs and white footed mice. (One nested in a bluebird house this year.)
    This study should have also used other plant material as a control, since I suspect barberry alone is not just what ticks live on.
    (In other words, tearing up all your barberry but leaving other plants won’t get rid of all your ticks.)
    This is an example of getting what you test for-not what is really happening in real life.

  20. I was concerned when I read the report blaming barberry bushes for the spread of Lyme disease thinking the barberry plant was the host to the tick. I have 9 barberry plants in my yard in clusters not as a thicket. After reading the report I decided that my few plants will not be any more of a problem than any ground cover or ivy my neighbors might have. I cut my barberry plants back to about 8 inches from the ground every year or two mostly to control the height but it also promotes the new pink foliage that I like. I do this late fall after the leaves have fallen or early spring so I can clean out around and inside the plant of any trapped leaves. It’s also very easy to remove any runners from the plant at that time. Although I’m not planning on planting any more of the thorny plants I do like the beauty of them and I won’t remove them.

    My hint on cutting the plants back is to take a very large tarp and wrap the tarp around the plant keeping the tarp a few inches off the ground. With both ends of the tarp together start rolling towards the plant. Use clamps at the rolled edge once you get the plant bundled and use your clippers at the bottom of the tarp to prune the plant about 8” from the ground. In the spring your plant will start to re-grow into a beautiful attractive natural smaller shaped bush and will grow from there. With the clamps in place and the plant still bundled you are able to carry the clippings to the truck to unload. If you put a large tarp in your truck before you start dumping your clippings when you get to the waste site all you need to do is grab the tarp in the bottom of the bed and pull it out of the truck and turn it over. This will save you countless scratches from the beautiful thorny bush.

    I’m pretty sure that the mouse will find any thicket to nest in. Blackberry, Ivy, low ground covers, or any plant that isn’t kept pruned a little off the ground. We have so many places in our yards that mice can inhabit and if they are the carriers of the tick I think we need to look at all possibilities and not blame a given plant. I think someone wrote that report after he got one of the nasty scratches from the thorns to rid the plants for our earth.

    JP of Washington

    • JP, Thanks for stopping by and commenting. If you read the report you’ll see Japanese barberry seems to be an issue because the mice’s regular predators don’t go into barberry thickets. I’m not sure if that’s the case with other thorny shrubs. Add to that, the highly invasive nature of Japanese barberry, at least here in CT, and the shrub has two very nasty strikes against it.

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  22. I haven’t seen a study on this before. We have Fat Pony Farm in Memphis, TN. We noticed that when we started removing our invasive species–in our case very dense Chinese privet and Japanese honeysuckle, with dollops of that blasted Bradford pear, Chinese lespedeza, and Nepalese browntop–our tick population drastically declined. We bought this completely overgrown 10 acres in 2007, started removal in 2008, planting more natives every year, added 6.5 acres in 2010 on which we increased field habitat, and mowed the enormous stand of bamboo. Every year there has been a reduction in pest insects–ticks, horseflies, mosquitoes. But especially ticks. We just thought the ticks liked the privet–when we take it out–it’s sterile–nothing seems to live in there at all. Also, when we moved here in 2007, it was silent. There were no birds. We are adding a couple of species back each year now. The sing and nest everywhere now.

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  24. Good morning! I am currently involved in some research on Lyme (am convinced I might have a potential cure…will keep you posted on that) and came across this information while researching the life cycles of ticks and Bb…
    I have a theory about another factor that might be behind this. Barberry and similar plants are excellent sources of a compound called berberine, which is very effective at dissolving biofilm. (Biofilm is a protective substance produced by bacteria that shields them from our immune response and from antibiotics…berberine was long thought to be an antibiotic, but it actually works by exposing the infective agent to our antibodies. It is extremely effective!)
    So my theory is that mice and other infected animals instinctively seek plants that contain berberine and other healing compounds…self-medicating in wild animals is a common and fascinating phenomenon, and could explain why we don’t find huge populations of debilitated animals, even though they are infected. They also don’t eat diets of processed “food” like we do…Our S.A.D. has a huge impact on our bodies’ in ate healing potential.
    Just thought I’d share! :)
    Would love a copy of the original study, please!
    Jeanette

  25. Hi Debbie,
    I am a Master Gardener in Lancaster Co PA and would like you to email me the info.
    It would be useful in answering questions of the public on our “Hort Line” and in one to one contacts. Thanks Lee

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