Barberry the Invasive

by Julie Barnes

A first time homeowner or new gardener wants a low-maintenance shrub at the local garden center that is cheap, attractive, hardy, and now more than ever deer resistant. Japanese Barberry, Berberis thunbergii would fulfill those needs. This ornamental plant was introduced into the U.S. in the late 1800's and was used to create a natural barrier in fields. It is sometimes used to construct a hedge. With its showy spoonshaped foliage, colored in burgundy or even chartreuse it stands out in specimen plantings. Exposure to full sun brings out the richest leaf color, but it is also very shade tolerant. Japanese Barberry is a dense shrub that grows 3-5ft.tall with spiny stems interwoven with small twigs and branches that deer absolutely avoid.

Small yellow flowers appear in spring followed by red berries in the fall that persist into winter, attracting birds and extending its season of interest. And, now that I have sung all the praises for Japanese barberry it is time to reveal a darker side. The hardiness of this resilient yard shrub also makes it a successful invasive plant. Birds and other animals eat the barberry fruit and deposit the seeds that germinate successfully at a high rate everywhere. Barberry also spreads through creeping roots or branches started by simply touching the ground. It has escaped from gardens and become naturalized forming dense green stands in forests, open woodlands, wetlands, and meadows thriving in diverse soil conditions, in sun or shade, heat or drought, and the coldest sub-zero temperatures. Growing unopposed by predators or
diseases, it crowds out native plants and reduces foraging habitat for wildlife once established. The Pennsylvania Department of Conservation and Natural Resources has already classified barberry on their invasive species list: It is not indigenous to our state and has a tendency to spread and displace native vegetation through its aggressive growth. Research from Chatham University has found that forests smothered by thick dense barberry growth have lower densities of native tree seedlings due to a lack of sunlight reaching them. Even a small patch of it seems to inhibit new native tree sprouts. Beyond this, the Japanese barberry also poses a danger in providing a safe haven for ticks carrying the Lyme disease pathogen.

Researchers in Connecticut have discovered that tick numbers are much higher in barberry infested areas. They have further established a connection linking Japanese barberry (Berberis thunbergii), blacklegged ticks, white-footed mice and white-tailed deer, thereby concluding:
• Spiny Japanese barberry out-competes native shrubs.
• Blacklegged ticks thrive in humid places, so dense barberry stands protect them in all their life stages.
•The Larvae of blacklegged ticks feed primarily on infected white-footed mice or other small host mammals benefitting from barberry's ideal habitat too; the thorny impenetrable structure shelters them from predators and provides abundant fruit for food.
• Diseased blacklegged tick nymphs or adults attach to deer passing by mature barberry bushes.
• Eliminating Japanese Barberry should reduce the number of blacklegged ticks and Lyme disease risk.

This past July the first meeting of the new Controlled Plant and Noxious Weeds Committee in the Pennsylvania Department of Agriculture was held. On the agenda to be discussed was whether, Japanese Barberry, the tick-harboring shrub should be banned in Pennsylvania? It's already banned in Maine, and Minnesota. West Virginia will do so in 2020. New York banned it in 2015, but made an exception last year for certain varieties that do not produce seeds. Other states have taken measures to control it. Before banning a plant like barberry committee members must consider ALL factors; threats to health, environmental damage, financial loss to growers and sellers, the plant's hardiness and showiness in people's landscapes, as well as, disease and pest resistance. Meanwhile, they suggest planting alternatives such as oak leaf hydrangea, red chokeberry, winterberry, Inkberry, or Virginia Sweetspire instead of Japanese barberry.