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When Bad Attracts Worse!

February 24, 2020 12:00 AM
By: Emily Domoto, Ecological Services Section Chief, Bureau of Forestry

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​Not only are invasives bad for native species, they often attract something else that can make a situation worse.

For example, the tree of heaven is the preferred host plant for the spotted lanternfly -- meaning the spotted lanternfly prefers to reproduce on this tree.

The invasive Japanese barberry isn’t attracting another invasive pest, but a pest that many Pennsylvanians try to avoid all year -- ticks.

About the Japanese Barberry

Japanese barberry lines road in state park

Japanese barberry (Berberis thunbergii) has been a popular landscaping plant for many years. This Asian native was introduced to the U.S. as an ornamental in 1875 when seeds were shipped from St. Petersburg to Boston’s Arnold Arboretum.

For more than a hundred years, while it’s been glamourizing neighborhoods, it’s also been escaping from cultivation.

At first, people were excited to plant it…it is pretty hearty.

Barberry is drought tolerant, grows in sun, shade, and wet areas. It also offers protection from people entering your yard with prickly thorns.

But this ornamental plant also has some nasty characteristics. It produces many seeds and has a high germination rate.

The seeds are not nutritious for wildlife, but they will eat them and deposit them, everywhere.

And since it can grow pretty much anywhere, it has been!

It has been taking over landscapes and forests from Northern Quebec to Georgia and moved as far west as Wyoming.

Whitetail deer grazing

Deer are also helping barberry spread. Deer eat many plants, but barberry is not one of them, which is helping to promote this invasive species.

As deer eat everything around the barberry, the barberry takes advantage and moves into those open areas.

This plant also changes the soil chemistry and pushes out native habitat.

Japanese Barberry Attracts Ticks

Black legged tick or deer tick

If you are still thinking of planting it in your backyard, think about this -- the prevalence of ticks infected with the Lyme disease is greater in areas with barberry than areas without.

A multi-year study in Connecticut looked at the relationship between barberry, white-tailed deer, white-footed mice, and blacklegged ticks.

The results are a bit alarming. The study found that the larger the number of barberry in an area, the higher the incidence of Lyme disease carrying ticks.

A Nursery for Ticks

Drooping clusters of pale yellow flowers develop on Japanese barberry in spring/early summer 

According to the study, barberry has denser foliage than most native species. As a result, the plants retain higher humidity levels which ticks love.

Ticks die from dehydration when humidity levels drop below 80 percent and do not rise back up. Lucky for ticks, relative humidity under a barberry at night is about 100 percent.

If that weren’t bad enough, the shrubs also provide nesting areas for white-footed mice and other rodents, which are primary sources for larval ticks’ first blood meal, and reservoirs for Lyme disease.

In addition to greater tick survival, ticks are more active in areas with barberry. In the open, ticks are active for 15-16 hours per day, but when they’re protected by barberry, that number increased to 23 or 24 hours.

So, in areas with barberry, ticks can hang out and wait for a host like you or me practically all day.

Invasive Species Impact Our Environment and Health

State park staff and volunteers dig up Japanese barberry

So, this aggressive invasive plant is not only pushing out native species, but it is also increasing the survival of a nasty, disease carrying arachnid.

The message is pretty clear: invasive species can affect our health and environment.

Please don’t buy or spread Japanese barberry, and if you already have them in your yard-go get your shovel!

Barberry is easy to identify in spring because it is one of the first shrubs to leaf out.

Using thick gloves, small plants can be pulled by hand, while larger plants should be dug up. Be sure to remove the entire root system and to bag and dispose of any plant material, including fallen fruits to prevent plant regrowth.

Learn more about Japanese barberry and how to control it, in a DCNR invasive plant fact sheet on barberry (PDF).

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