Lyme-ticks thrive in Japanese barberry thickets

OLYMPUS DIGITAL CAMERA This time of year the undergrowth of Connecticut woodlands begins to show a tinge of green. This color is certainly welcome relief after a long winter. Too bad so much of this color is due to invasive Japanese barberry (Berberis thunbergii de Candolle). This thorny shrub dominates unmanaged wooded areas. Deer don’t eat it and birds spread it by eating and dispersing the shrubs’  prolific fall berries. Japanese barberry quickly grows into large thickets that provide cover for mice and an ideal environment for immature blacklegged ticks -  the very ticks that carry Lyme disease. In their early life, ticks are susceptible to desiccation – they need high-humidity at the ground level to thrive. Japanese barberry accommodate young ticks by leafing out earlier than most native shrubbery. The early leaves help maintain moisture levels at ground level by blocking drying sunshine.

This connection may not be a big deal if a tick simply lived its entire life in a barberry thicket. They don’t. After ticks feed on mice they seek out host number two – commonly white-tailed deer. Fortunately for the ticks, Japanese barberry grows to a height that allows them easy access to passing deer. Ticks climb barberry stems where they hitch a ride on passing deer.  Deer stroll from woodlands to yards and gardens, bringing their tiny passengers along for the ride.

OLYMPUS DIGITAL CAMERA We know this, in part, because of research from the Connecticut Agricultural Experiment Station in New Haven. Scott C. Williams and Jeffrey S. Ward have been monitoring the number of mice, the number of ticks and Lyme-infected ticks, and ground-level humidity in three geographic areas of Connecticut. In each area they have test plots of uncontrolled, controlled, and no Japanese barberry. For control, they used one of three methods.

One form involved torching the base of each shrub until the main stems carbonized and glowed – in effect girdling main stems to stop nutrient transfer. The dead shrubbery was left standing. The other two forms of control involved mechanically cutting the shrubs – usually by brush hog – and mulching cut plant material in place. They controlled regrowth with herbicides or flame from a propane torch applied directly to new sprouts. Note: Torching is acceptable control method for organic land care. It involves heating new sprouts by sweeping the  flame back and forth over leaves until their cells burst –  torching does not involve turning a large patch of land into a  flaming inferno. 

With a total of three years of data now collected, Williams and Ward estimate plots without barberry have 30 Lyme-infected ticks per hectare (the equivalent of 2.471 acres). By contrast, plots of uncontrolled Japanese barberry contain 280 Lyme-infected ticks per hectare.  They report decreased humidity and suspect this led to “a near 60% reduction in the number of B. burgdorferi-infected adult blacklegged ticks,” in controlled plots.

They speculate continued barberry control will result in continued decline in tick populations and, therefore, suggest all landowners, managers, stewards “immediately initiate a management plan to address this alien invader.”

As Scott Williams explained for my report on his and Ward’s previous Japanese barberry-tick study, mechanical control takes vigilance and follow-up. Effective eradication requires proper identification, mechanical removal of all above-ground portions in late-spring or early summer, allowing the shrubs’ roots to use starchy reserves to force out new growth, then killing new growth in later summer. (Again, propane torch flaming is an acceptable organic land care practice.)

OLYMPUS DIGITAL CAMERA Do not cut barberry and expect it to die. As Williams notes, cut shrubs send up new growth with a vengeance.

Williams also advises against pulling a barberry shrub from the ground unless it is small and you can get all the roots. Any little rootlet may re-sprout. Again, re-checking for re-sprouting is vitally important.

I urge homeowners to take a few minutes to check their properties for Japanese barberry and, if found, to follow the control methods described above. This, and not planting any more Japanese barberry, may just cut your chances for Lyme disease.

Read more on Japanese barberry:

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14 comments for “Lyme-ticks thrive in Japanese barberry thickets

  1. April 17, 2011 at 7:41 am

    As always, you give great detailed info. Even in this cold bitter spring, I have come into the house and found a tick on me… and that was early April. Is there no dormant season? After a horrendous bout with raging Lyme, paralysis and high fever in 2008, I panic at the sight of ticks.

    Barberry is only just starting to show up in my weedy meadow, just a few plants so far. I have been pulling them out, but your info is good to know on how that might not be effective.

    • joenesgarden
      April 17, 2011 at 9:36 am

      Laurrie, the key to control is regular vigilance. I plan to walk my woods to ID and eradicate any Japanese barberry I’ve missed on prior walks. I’m fortunate to not have alot of the shrub. I’d like to keep our woods completely clear. I’ve had Lyme disease too and I don’t want to live through that again.

  2. April 17, 2011 at 11:07 pm

    I’ve heard that Guinea fowl will eat ticks, they might be something to consider keeping where there is a problem. Here is an article I found on google.

    • joenesgarden
      April 18, 2011 at 5:45 pm

      Thanks for your comments and the link, Hannah. I had heard that also but that tidbit of info was debunked during my recent Organic Land Care class. We were told that Guinea fowl can be tick hosts and thereby spread ticks. Ticks can use birds and other mammals besides deer for one of their life cycles.

  3. April 19, 2011 at 4:54 pm

    Joene, I just want to tell you how valuable I find your careful reports on environmental research studies like this one. The part of Pennsylvania where I live during the school year (Adams County) has very high rates of Lyme Disease. (I have colleagues whose whole families have suffered disabling effects of infection.) The more we know about the life cycle of the deer tick, the more effectively we can fight this disease. Thanks for the education.

    • joenesgarden
      April 20, 2011 at 5:49 pm

      You are very welcome, Jean. It’s so important to get information like this out to people … this is my small bit of public service.

  4. April 23, 2011 at 12:31 pm

    Williams advises against cutting and against digging up, but he didn’t really say what he would advocate, which I hope won’t give people the idea they should use some sort of herbicide.

    I eradicated most of the barberry growing on my 1.5 acres many years ago, but recently noticed a few that have spread or reappeared. Perhaps I can get to them.

    • joenesgarden
      April 23, 2011 at 5:17 pm

      Hi fern,
      In my emails with Scott Williams he advises against digging up large barberry shrubs unless one is vigilant in returning to that spot and eradicating any new growth. Pulling up small shrubs – say a single stem – is better than leaving them in place but, again, folllow up is necessary since any rootlet can resprout. Torching is effective in destroying regrowth after cutting – this is the way to deal with large stands or large shrubs.

  5. April 23, 2011 at 5:39 pm

    I don’t think the fire dept would appreciate it if homeowners start torching burning bushes. I’m sure they would advise against it for safety reasons.

    Even if someone is not vigilant about returning to check a spot where they dug up a large shrub, surely, digging up the shrub itself is far better than doing nothing, no?

    • joenesgarden
      April 23, 2011 at 6:26 pm

      Fern, torching to kill an invasive plant or a weed does not involve burning the plant with active flames, such as setting a bush on fire. You wave the flame of a propane torch back and forth over the leaf surfaces until the cells in the leaves burst. This prevents nutrient/water exchange and plant death. You do not set the plant/shrub on fire. The term torching is unfortunate, but this is the term used for this process.

      Because underground rootlets so often resprout, digging or cutting without follow up is likely to cause many more Japanese barberry plants to grow. Whether you dig or cut these shrubs, you MUST check the spot a few more times each season to further eradicate regrowth. Regrowth comes back with a vengence, in Scott Williams’ words. There is no easy answer here. It’s a nasty invasive that is not easy to eradicate.

  6. April 24, 2011 at 8:19 am

    OK. Guess I learned something new today. Still, waving a propane torch around plants sounds dangerous. You could easily catch leaves or other debris on fire. Sounds ok if you were the caretaker of a nature sanctuary, but for the average homeowner, i don’t think it’s a good idea.

    But thanks for the explanation. I had never heard about doing that before.

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