Invasive plant found to harbor large tick populations

Its colorful foliage and red berries hide a darker purpose as an ideal lair for the black-legged tick.

Japanese barberry is an invasive species that was introduced into the United States in the late 1800s. The plant is popular for landscaping projects because of its colorful foliage and red berries. It has also been seen as a natural barrier on properties due to its thorn-covered branches. However, the plant is more than just aesthetic -- it also is home to significant black-legged tick populations.

Connecticut Agricultural Experiment Station Scientist Scott Williams said the plant is a natural nursery for ticks because it traps and retains humidity underneath the canopy of its branches.

"Ticks are prone to drying out and Japanese barberry creates a mid- to lower-level canopy that retains humidity throughout the day," he said. "We've found that ticks in Japanese barberry had a higher percentage of the Lyme bacteria."

Williams believed the higher percentage of infected ticks was due to feeding on infected mice as they grow and spreading the disease to even more mice.

"It's pretty interesting to have a plant that is so harmful to human health and the environment," Williams said.

One of the biggest issues with the plant is its ability to overwhelm native flora and its resiliency.

"The best way we've found to get rid of it is to cut it off low to the ground in its early growth stage and then spray it with herbicide or use a propane torch. People just need to remember to be careful when using the torch and not start a forest fire," he said.

Once the plant is moved from an area, Williams said studies have found the tick populations decrease significantly. Adult ticks also decrease in numbers once the plant is removed.

In a 2010 study conducted by Williams and Jeff Ward, they reported they found:

210 black-legged ticks per acre in Japanese barberry stands;

92 per acre where they removed Japanese barberry;

35 per acre where Japanese Barberry did not grow.

It was also reported that the number of ticks infected with Lyme disease was, reduced when Japanese Barberry was removed:

- 113 deer ticks infected with Borrelia burgdorferi/acre in Japanese Barberry stands;

- 49 infected ticks/acre where they removed Japanese Barberry;

- 12 infected ticks/acre where Japanese Barberry did not grow

"Japanese Barberry is quite prevalent all over the state and it prefers abandoned agricultural fields where livestock were raised," Williams said. "You need to keep monitoring it even after removal because it can spread from birds eating the berries and then pooping somewhere else."

Although birds do enjoy eating the berries, Williams said the plant spreads more rapidly when a limb touches the ground and it can spread more roots.

"It needs a lot of sunlight in order to grow and Connecticut has a pretty mature forest, so there isn't a lot of sunlight that hits the forest floor," he said. "We've found it spreads through layering because it can spread more roots through a branch that touches the ground."

Japanese Barberry's progress is also assisted by local deer populations, which will not eat the plant.

"Deer don't eat Japanese Barberry but they will eat the surrounding plants and it kind of gives an edge to the Barberry," Williams said.

Friends of Animals Outreach Coordinator Nancy Rice said Japanese Barberry is an important aspect in the battle against Lyme disease.

"This is another example of the info that isn't always provided that might give another piece of the puzzle," she said. "This information needs to be presented to the public."

Deer Management Committee Chairman Kent Haydock said in an email that the plant is a problem because of the prevalence of ticks living beneath its canopy.

"After adult female ticks get on deer, they lay many thousands of eggs. Then, after they hatch, tiny juveniles fall off into grasses and underbrush. There they are apt to get on mice, chipmunks and some ground-nesting birds. The barberry are used for illustration, as being thorny, they easily catch ticks off passing deer. Also, we hear that mice are apt to live in barberry bushes," the email stated.

Haydock also said the juvenile ticks are more likely to remain beneath the canopy of Japanese Barberry because they feed on smaller animals, whereas the adult ticks prefer larger blood meals.

"Juvenile ticks are apt to stay feeding there until they become adult ticks, as adult ticks do not feed on such small critters. Most importantly, adult ticks then feed on deer, where the life cycle restarts," he said in the email.