Look into the woods of Connecticut during early spring and you’ll likely notice stands of low-growing shrubs leafing out in an almost eerie lime-green. It’s likely Japanese barberry (Berberis thunbergii DC) at its worst – invading our woodlands.
These imports from Japan now dominate large expanses of woodland undergrowth and crowd out native trees and plants – reason enough to find the thorny invaders objectionable. But scientists have uncovered more rationale to abhor the shrub; dense Japanese barberry thickets serve as favorable breeding grounds for Lyme disease-carrying ticks.
Scott C. Williams, PhD, and colleagues at The Connecticut Agricultural Experiment Station in New Haven compared three plots of land in Connecticut. They left one heavily infested Japanese barberry plot alone. In a second plot Williams’ team controlled barberry thickets by cutting the shrubs down, then killing late-summer new growth with a propane torch. Their third study plot had no evidence of Japanese barberry.
William’s team spent two years trapping and recording the numbers of white-footed mice in each plot, as well as the number of ticks feeding on the mice. They found the uncontrolled thicket of Japanese barberry averaged 6-to 7-times more ticks over the two years than the other two plots.
Barberry thickets give mice protection from predators serve host to one part of a tick’s life cycle. William’s group speculates the early spring leaf-out of barberry thickets creates the humid ground-level micro-climate in which ticks thrive. These two factors seem to give ticks a good jump start. Once done feeding on mice, barberry shrubs provide ticks the avenue – so to speak – necessary for the little blood suckers to complete another life-cycle phase. By climbing to the upper regions of the barberry shrubs they are able to catch a ride on passing deer.
Now if deer ate Japanese barberry, I doubt the shrubs would be so prevalent. But deer don’t like the thorny invaders any more than humans, so Japanese barberry thrives, mice thrive, ticks thrive, and deer certainly thrive in Connecticut woodlands. The combination may create the perfect Lyme-disease storm.
But before you grab a machete or other instrument of destruction to attack barberry thickets, understand the shrub is not easily controlled. Williams suggests a two-step process:
· First mechanically remove the above ground portion of the shrub in spring or early summer. For heavy stands a brush saw or tractor-mounted brush hog works best.
· Then allow the shrub to use some reserved energy to shoot-up new growth. In late summer kill new growth with either an herbicide or a propane torch.
The second step is vital. Left alone the shrubs will grow back “with increased vigor,” Williams told me in an email. Forget to follow up and after one growing season your cut-down barberry thicket will look like you’ve done nothing.
Hand pulling might work if you are lucky enough to find just a few small barberry shrubs in your area. “It’s a heck of a lot easier to get rid of them before they form an impenetrable thicket,” Williams said. But “any little rootlet left in the soil has the potential to re-sprout into a mature plant.”
Again, regular vigilance is needed to eradicate Japanese barberry.
The Invasive Plant Management Guide from UConn offers more detailed Japanese barberry obliteration methods. Click on the Woody Plant link, then on Japanese Barberry. Additional photos from Invasive Plants of the Eastern U.S. will give you a better idea of the shrub’s many stages, including the bright red berry stage. Birds eat the berries, do their bird do-do from whatever perch they choose, and voila, barberry spreads.
Massachusetts prohibits the sale of Japanese barberry. There’s some move toward a voluntary ban on sales of certain Japanese barberry cultivars in Connecticut. All homeowners, gardeners, and landscapers should avoid buying and planting Japanese barberry.
Personally, I don’t understand why anyone wants these shrubs in their landscape – I have yet to see a cultivar I find attractive. Considering the negatives, doesn’t it make more sense to just avoid planting Japanese barberry?
Stay tuned. Debbie, at A Garden of Possibilities, plans to alert readers on any ban updates in Connecticut, and Williams told me he is in the process of compiling information from continued samplings of the original plots. His team has also continued to manage barberry thickets using only propane torching and he plans to report on these findings as well.