The problem has risen with the trade in live plants, with imports now valued at $500 billion annually, the University of California, Santa Barbara, reported Monday.
In the last 43 years, the quantity of imports to the United States has risen by more than 500 percent, peaking at 3.15 billion plants in 2007, with nearly half destined for either California or Florida, researcher Andrew Liebhold said.
Imported insects and disease, once introduced, quickly become established and some of them become major pests with economic consequences for U.S. forests, he said.
One example is Sudden Oak Death, caused by the pathogen Phytophthora ramorum, and introduced into the Bay Area and Big Sur regions of California via nursery plants.
The disease has now spread through 14 counties in California, as well as southern Oregon, where it has caused large-scale die-off of oak trees.
"The demand for live plants from outside the United States is not likely to diminish," Liebhold said. "As global trade expands, our knowledge of pest pathways must be improved to ensure trade is accomplished with minimal environmental degradation."