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.
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.
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.
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.
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.
Great post, glad I found this blog.
[...] To learn about the Japanese barberry and its link to Lyme Disease, click here. [...]
[...] To learn about the Japanese barberry and its link to Lyme Disease, click here. [...]
[...] been linked to a high prevalence of Lyme Disease. If you are unaware of the relationship between Lyme Disease and Japanese barberry, you will probably find this post quite interesting. [...]
Please forward the pdf on Japanese barberry and Lyme. Thanks.
Hi Mark, I just emailed it to you.
[...] little knowledge can go a long way. But before you rush out to buy Japanese barberry, click here to read about the surprising relationship between Japanese barberry and Lyme [...]
Please send me the PDF on Japanese barberry and Lyme Disease. Thank you for posted it!
Shami, I just sent it to you. Good luck with your project.
[...] I decided to write about Japanese barberry (Berberis thunbergii), a plant that has been on my hit list for years. I’ve written about Connecticut’s voluntary phased-in ban of 25 different Japanese barberry cultivars and also about an ongoing study happening right here in Connecticut that looks at the surprising link between Lyme disease and Japanese barberry. [...]
[...] A multi-year study, taking place in Connecticut, is looking at the relationship between Japanese barberry (Berberis thunbergii), white-tailed deer, white-footed mice and blacklegged ticks. The results were recently released from the first two years of the study and 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 carr…. [...]
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.
I’m so heartened that you answered my note! I would love a copy, definitely. Thank you. Abigail.
Abigail, Answering comments is part of the fun of having a blog:) I just emailed you a copy of the study.
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.
I’m looking forward to some interesting and thought-provoking comments from you, Abigail!
[...] disease. Debbie over at A Garden of Possibilities covered this topic in 2009 in a post entitled ‘The Surprising Relationship Between Lyme Disease and Japanese Barberry’, a very interesting [...]
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.
Could I get a copy of that study?
I’m emailing it to you now.
[...] they are also highly invasive in many states, are known mice hotels and there has been a link established between Japanese barberry and Lyme Disease. But before you go out in the garden and chop them down, check out this info from UCONN on proper [...]
debbie
thank you for your timely article. question; does the common barberry have the same threats as the japanese barberry. ( lyme disease related ).
thanks Tom Lewis
tlewis15@optonline.net
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.
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?
Mark, I emailed the report to you, please let me know if you didn’t get it. Best of luck resolving your deer problem.