Shrub threat level increasing

By Marianne C. Ophardt, Special to the Herald

KENNEWICK -- The "terrorist" or invasive plant threat level has been raised to "red."

They're popular plants in our landscapes and seem so innocuous. It's shocking to find that common ornamental shrubs that have been around for years are a threat to the native plant and wildlife in our country.

One of these invasive "terrorists" is Japanese barberry (Berberis thunbergii), a native of Japan. It first infiltrated this country in 1875 when some of its seeds were sent to the Arnold Arboretum in Massachusetts. In 1896, Japanese barberry shrubs were planted at the New York Botanic Garden. It was later promoted as a substitute for the common barberry (Berberis vulgaris), also a non-native from Europe.

The common barberry was used by European settlers for creating hedgerows, as well as for making jam and dyes. Unfortunately, common barberry was discovered to be an alternate host for black stem rust, a devastating fungal disease of wheat in this country.

After two serious wheat stem rust epidemics in the early 1900s, the Department of Agriculture initiated a program to eradicate common barberry in wheat producing states.

By 1933, more that 18 million barberry shrubs had been destroyed. It wasn't easy. This European native shrub, planted by European settlers, had escaped its original planting sites and had become invasive, just like its Japanese cousin has done more recently.

The eradication program was a success with 98 percent of common barberry shrubs eradicated in the targeted areas by 1972. In 1981, this successful federal program was discontinued. If it hadn't turned out that the Japanese barberry was stem-rust resistant and didn't pose a hazard to wheat, it might not have become a popular landscape shrub.

It became a replacement for common barberry because of rust resistance. Plant breeders have worked with Japanese barberry, creating numerous colorful cultivars available for today's landscape plantings.

Over the years, the Japanese barberry's popularity has grown.

Unfortunately, that's not good news. Jil M. Swearingen, M.S., the Invasive Species Management Coordinator for the National Park Service, points out that Japanese has become invasive in 20 states in the northeastern U.S.

Swearingen notes that Japanese barberry forms dense thickets in many different natural habitats, including canopy forests, open woodlands, wetlands, pastures, and meadows. By displacing native plants, the Japanese barberry reduces wildlife habitat and forage.

How does it spread? You know those clusters of little bright red berries that develop after the pale yellow flowers fade in the spring? Birds and small mammals eat the berries and spread the shrub via the seeds in the berries. The shrubs also multiply from parts of roots left in the soil when the plants are removed.

Is it a problem in Washington? Not so far. Japanese barberry is not on noxious weed lists in Washington, however it has the potential of becoming a problem in some areas of the state. It has become a problem elsewhere because it's very adaptable. It prefers full sun, but is shade tolerant. It's drought resistant, but will also grow in wetlands.

Should we stop selling, buying and planting Japanese barberry here? I think in our local area with an arid climate, it should not be considered a serious threat.

Personally, I've never been a fan of Japanese barberry. I don't like plants with red-brown leaves, and I can't abide with any spiny, thorny shrubs -- except for roses.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension Office.

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Saturday, Sep. 05, 2009

Shrub threat level increasing

By Marianne C. Ophardt, Special to the Herald