In fall of 2021 two popular landscape plants were added to the Pennsylvania Department of Agriculture’s list of noxious weeds: Japanese barberry (Berberis thunbergii) and Callery, or ‘Bradford’, pear (Pyrus calleryana) . According to Pennsylvania law a noxious weed is “a plant that is determined to be injurious to public health, crops, livestock, agricultural land or other property.” Most plants on the noxious weed list are recognized nuisances (for example, Canada thistle, poison hemlock, and stiltgrass). However, Japanese barberry and Callery pear trees have long been promoted for residential and commercial landscaping. Their placement of the noxious weed list includes a phased plan for making their propagation and sale in Pennsylvania illegal.
Why is Japanese barberry a problem?
Known for its dark red foliage and deer resistance (due to thorns), this seemingly well-behaved shrub forms dense thickets in natural areas, crowding out diverse ecosystems of native plants. Japanese barberry has berries that many people do not even notice. Birds eat these berries and then disperse them in meadows, pastures, and woods. Japanese barberry also spreads when its branches touch the ground and root. Some research indicates that Japanese barberry harbors the black-legged tick, a major source of Lyme disease.
Why are Callery pear trees a problem?
The Callery pear was developed as a street tree in the mid-20th century; landscapers and residents embraced the trees’ flush of white blossoms in spring, rounded canopy, and attractive fall color. Despite their pleasant appearance, they have proved to be very susceptible to wind damage. Like Japanese barberry, Callery pear trees originated in Asia and have escaped cultivation in North America, aggressively taking over natural areas. Birds and small mammals consume the small, hard pears—inedible to humans—and distribute the seeds. The trees also spread through a shallow root system.
What can residents do?
By fall of 2022 Japanese barberry and Callery pear trees should be difficult to obtain in Pennsylvania because of a phased plan by Pennsylvania Department of Agriculture to eliminate propagation and inventory at nurseries. (Detailed information on the plan to eliminate sale and propagation for each plant is contained in the links at the end of the article.) At this time residents are encouraged, but not required, to remove existing plants. Though sterile cultivars of Japanese barberry may be available soon, Master Gardeners recommend that residents choose native plants as replacements or additions to the landscape.
Native plants to replace Japanese barberry:
- Ninebark (Physocarpus opulifolius) has burgundy foliage and peeling bark that adds winter interest.
- Smooth hydrangea (Hydrangea arborescens) is a native version of the popular shrub.
- Virginia sweetspire (Itea virginica) sports cylindrical, aromatic spring blossoms and lovely fall color.
- Inkberry (Ilex glabra) is a broadleaved evergreen in the holly family that has a hedgelike quality similar to Japanese barberry.
Native, spring-blooming, replacements for Callery pear:
- Serviceberry (Amelanchier canadensis) has lovely, white spring blossoms and berries attractive to birds.
- Redbud (Cercis canadensis) is known for its purple spring flowers; white cultivars are also available.
- Crabapple (Malus, spp.) Though both native and exotic varieties of crabapples are available, according to Doug Tallamy in Bringing Nature Home, natural hybridization has helped make most crabapples friendly to native wildlife.
For more native plant suggestions and advice on removing invasives, please reach out to your county Garden Hotline. See the Penn State Master Gardener Program webpage for a directory.