More Findings on the Link Between Japanese Barberry and Lyme Disease

Japanese barberry infested forest in Spring.

Japanese barberry infested forest in Spring. © Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Recently, I attended a symposium where current research findings on the link between Japanese barberry (Berberis thunbergii) and Lyme disease were presented. Over the past few years we’ve learned that this highly invasive non-native shrub is not only impacting our regional ecosystems, it’s also indirectly affecting our public health. While Japanese barberry is considered invasive in at least 20 states and the District of Columbia, it is also still available for sale in many nurseries across the US.

According to recent studies by scientists Jeffrey Ward and Scott Williams at the Connecticut Agriculture and Experiment Station (CAES) eliminating stands of Japanese barberry from forested areas can  reduce the number of  Lyme disease-infected ticks on the property by 80%.

The Problem With Japanese Barberry

Once established, Japanese barberry tolerates a wide array of site conditions, from full sun to shade and it’s not overly picky about soil conditions. It reproduces through seeds, rhizomes or layering and  forms dense thickets that choke out native wildflowers and tree saplings.

Japanese barberry flowers

Japanese barberry flowers are prolific seed producers. © Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Berberis thunbergii is a prolific seed producer and it’s seeds are estimated to have a 90% germination rate. Birds eat the seeds and carry them for a few hundred yards, depositing them in areas where the Japanese barberry can take hold and quickly choke out most other plants.

Breeding programs to develop ‘sterile’ Japanese barberry cultivars may be misguided since past history with other sterile cultivars of invasive plants has shown they sometimes cross-pollinate with the wild species.

The Link Between Japanese Barberry, Ticks and Lyme Disease

Ward and Williams’ research has shown that  Japanese barberry infested forests have approximately 120 ticks infected with the Lyme disease bacteria per acre. Compare that to approximately 10 infected ticks per acre found in forested areas with native trees and shrubs and no Japanese barberry.

It seems that stands of Japanese barberry retain humidity. And ticks need an environment with about 80% humidity to actively feed, quest and reproduce.  By measuring humidity levels above and at ground level under the barberry foliage, Ward and Williams found humidity levels under Japanese barberry dipped below 80% for only one hour per day. In open, sunny areas with no Japanese barberry, the exact opposite is true. The humidity levels rise to 80% for only one hour each day.

White-footed mice, a known apex host for Lyme disease also thrive under the canopy of Japanese barberry. The combination of mice and a tick population this is active almost all day long appears to be a potent mix that is leading to a public health epidemic in many states.

Why You Should Care

At this point, you may be thinking so what? I don’t have Japanese barberry in my garden and I don’t live near or spend time in a forested area with lots of Japanese barberry so how does this affect me.

In addition to creating the ideal environment for ticks, stands of Japanese barberry also tend to increase the levels of nitrogen in the soil. At the same time, the number of earthworms in the nearby soil almost doubles.

In our gardens, earthworms are welcome visitors. But in Japanese barberry infested forests, they are devouring the leaf litter which should act as a protective covering for the soil. Less leaf litter means loose soil, more erosion,  less tree regeneration and less wildflowers.

Nitrification and low levels of leaf litter also add to storm water run off which affects the quality of water in our reservoirs. If you drink water, you should care about Japanese barberry infestations.

Controlling Japanese Barberry

Japanese barberry infested forest

Japanese barberry infested forest. © Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

The team at CAES worked on 150 acres of land divided into 28 different study areas. They evaluated 56 different treatment and timing combinations for controlling Japanese barberry and found that a fairly simple two-step process is most effective.

First, kill all of the plant that is above ground by cutting it down or applying heat with a propane torch. Before you run out and buy an industrial flame torch, please read these safety guidelines from CAES or check out this video on controlling barberry.

Next, once the roots begin to push out new growth, treat this growth with heat or a chemical herbicide. Here in Connecticut, starting this 2nd step in  mid-October seems to be ideal. The plant is already stressed so the second attack will likely kill it. If the barberry you’re eliminating is mature, you may need to continue step two a few more times.

The size of the area you’re treating, the density of the Japanese barberry and your comfort level using propane and/or chemicals should dictate how you actually proceed. Ward and Williams also found using a chemical herbicide worked best for controlling plants growing in full sun.

Be Ready to Plant

The flowers of dwarf witchalder, a native alternative to Japanese barberry.

The flowers of dwarf witchalder, a native alternative to Japanese barberry.

The third step in controlling Japanese barberry is to be ready to re-plant the area with native plants. This is an important step for increasing biodiversity.

If you don’t re-plant quickly then it’s quite possible other invasives will move into the area and you will have traded one problem for another.  If deer are a problem, plant only deer-resistant natives or fence off the area.

Some native shrubs that are good alternatives to Japanese barberry include highbush blueberry (Vaccinium corymbosum), New Jersey tea (Ceanothus americanus), Virginia sweetspire (Itea virginica), and dwarf witchalder (Fothergilla gardenii).

© 2013, Debbie Roberts. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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Comments

  1. Rob Halpern says

    You offer no link to the study, so forgive me if this comment is misguided.
    Berberis appears implicated because it is a deer resistant dense woodland-tolerant shrub. Nothing specific to Berberis (let alone B. thunbergii) is seen as contributing to tick populations. So how do you recommend replacing Japanese barberry with native shrubs? In this case, if the deer do not decimate the natives then you have re-created the very environment that the berberis provided.

    The reasoning is faulty.
    One perhaps ought to conclude that eliminating a shrubby understory in the forest is the best solution. Why do you not explore that?

    • says

      Rob, You’re right, I did not provide a link to a study because I couldn’t find a current one that is available without a paid subscription to a scientific journal. The two scientists referenced , Dr. Ward an Dr. Williams, have been studying this link for years and there are numerous references to older studies online. If you would like a pdf copy of an older study, on which these findings are built, please email me and I will be happy to provide it to you.

      If you read my post you will see that I do reference some very specific issues with JB that contribute to its link to Lyme disease, most notably the increased levels of humidity under its canopy.

      In regards to replacing JB with native shrubs, it sounds like you are assuming that ALL native shrubs are browsed by deer. It’s true that some native shrubs are deer candy and care must be given to replacing JB with deer-resistant natives if deer are an issue. While deer browsing varies greatly by region, and even from garden to garden, in my own garden highbush blueberry and Virginia sweetspire are not browsed by deer.
      Debbie Roberts recently posted..Wordless Wednesday ~ Upside Down

      • Rob Halpern says

        Thanks for the reply Debbie.

        I do not mean to defend Japanese barberry or invasives, but rather to urge us to keep our critical thinking sharp.
        If humidity levels under a shrub such as Japanese barberry are high, it is a fair guess that humidity is almost as high under other similarly structured shrubs, native or introduced. Unless a comparison is made between Itea and Berberis, there are no grounds to use these findings to recommend Itea.

        The case for natives must, IMO, be made on their actual merits not merely on assumptions. Using these findings to tout natives over invasive introduced species is bad science. The evidence for it is simply not in this research

        • says

          Rob, I agree that critical thinking around this question of invasvive plants is crucial and I enjoy the back & forth in these types of forums. I think the conversation is helpful to everyone.

          While I am not a scientist, it’s my understanding that the issue with the humidity levels under JB and its impact on Lyme disease infected ticks has to do with layering growth habit of JB and the way that mice predators do not venture into JB. I’m assuming that has to do with the thorns but I’m not entirely sure if that’s the only reason.

          It’s not just high humidty levels leading to increased #’s of Lyme disease infected ticks. It seems to also have to do with JB being a safe haven for white-footed mice. I don’t know of any other shrub – native or non-native that offers the same protection. So high humidty levels under the JB leading to an active tick population, coupled with lots of mice makes the transmission of the Lyme disease bacteria more prevalant.

          Ward & Williams were asked if the # of ticks in other forested areas with a monoculture (the example was ferns) was also high. Their answer was that they don’t know for sure since there hasn’t been funding for that type of research. And based on limited anecdotal evidence from spending time in fern infested areas there does not appear to be a clear answer. Even if they did find that there were higher #s of ticks, would those ticks have such a high rate of infection? For now we don’t know but we do know that there is a direct correlation between JB and Lyme disease, which IMHO, is important information to disseminate.
          Debbie recently posted..Wordless Wednesday ~ Upside Down

  2. Sue Sweeney says

    Debbie — There is absolutely no need to use herbicides, especially broadcast sprayed. Further, never ever use a flame thrower unless you can recognize all forms of poison ivy, including last year’s dead stuff on the ground. I have to question the motives of the Ag Station in making these recommendations, especially to homeowners who don’t know the full range of choices available and haven’t been fully apprised of the dangers involved. The Ag Station’s method might be the faster for a large spread but at what cost to health and environment? It is totally unnecessary to take these risks for an isolated plant or a small spread.

    Barberry is easily controlled by ground cutting every few years. A few bushes, and all younger plants, can also easily be up rooted. (If left in place, turn them upside down to prevent re-rooting). If one must take out the herbicides, despite the health risks, cut the barberry to the ground in late summer or early fall , then carefully paint herbicide on the cut ends.

    Planting in natural areas or yards abutting natural areas is OK if the added plants are local genotype natives (e.g from Earth Tones Nursery or another CT nursery specializing in local natives)- and even then no garden cultivars, please! Otherwise, the introduced stock may corrupt our local natives. If re-planting, be ready to water for at least two years. Alternatively, monitor the area monthly, removing invasive as they appear and leaving whatever natives show up on their own to grow naturally. Be care of further soil disturbance or compaction (good to use stepping stones or the like to access the area).

    Sue

    • says

      Hi Sue, Thanks for the tips on using local genotypes and the need to constantly monitor for invasives. I agree that herbicides should not be the first choice for controlling JB but I defer to the experts on the most effective and efficient way to control it, especially JB that is growing in full sun. For land managers and homeowners who have many acres of land, the cost/benefit of controlled use of herbicides is a decision they must make for themselves.

      If you follow the link to the video on controlling JB, you will see that all of your concerns are in fact addressed. The scientists featured in the video are very conscious of safety for both themselves and the environment and certainly discuss issues such as not broadcasting herbicides (they actually talk about how cutting the plant down first greatly reduces the amount of herbicide that is applied) as well as proper use of propane torches.
      Debbie Roberts recently posted..Wordless Wednesday ~ Upside Down

  3. says

    Thanks for this article.

    I’d like to add several native species for consideration for planting following the removal of Berberis thunbergii from the forest floor:

    Spicebush (Lindera benzoin)
    Black Huckleberry (Gaylussacia baccata)
    Blue Huckleberry/Dangleberry (Gaylussacia frondosa)
    Hobblebush/Moosewood (Viburnum alnifolium/lantanoides)
    Hazelnut, either American or Beaked (Corylus americana or cornuta)

    Details about these and other species were mentioned in a talk I recently presented at the 2013 RI Land and Water Conservation Summit. The native species PowerPoint and handout from that presentation are accessible at this link: http://www.landandwaterpartnership.org/summit2013.php

  4. Heath says

    I had no idea! Cannot believe they are still selling this at garden stores! Please do not use Roundup (brought to you by the agent orange creators at monsanto) or any other corporate “herbicides”. They contaminate the groundwater! Not to mention a large percentage of women and newborns are being found to have glycophosphate in their bloodstream! This is not good for humanity or the planet! If you are battling a weed first try boiling water. Then white vinegar if the water didn’t work. Baking soda works well in my bricks around the herbs. I just use a big box and everything is brown the next day. You can also try saltwater if you do not want anything to grow there again.

    • Bart says

      I know people are well meaning and this is a respectful site, but I find that too many people here seem to be focusing too narrowly on their own tiny garden plots rather than relating to the actual problem of lyme disease in general. We need to address how to remove this particular invasive from large areas (many acres or square miles) while doing the least amount of damage possible. While it is true that boiling water is fine for a tiny plot in a back yard, and seems like a fine solution there, it does not begin to address the landscape level problem we are facing here. I applaud the efforts of Debbie in making the results of recent research available and I am certainly skeptical of solutions proposed by self interested corporations, but please try to think of yourselves as part of a larger community of concerned people trying to address this problem rather than only asking how does this affect me personally or my garden. This is how we got into this problem with folks planting any exotic willy-nilly because it seemed attractive without considering others or the larger environment. It may also be true, as suggested by an earlier respondent, that removing this invasive may not solve the Lyme disease problem, but I say, it couldn’t hurt.

  5. gina says

    I live in northcentral Wisconsin and have a terrible problem with Japanese barberry. There is another tick borne disease that has been showing up here and has already infected most of the dogs in the area. It is Anaplasmosis, and the symptoms seem to be quite similar to Lyme’s. Needles to say, I am going to go outside and start cutting back the barberry immediately.

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