Plant pathologists across the United States are scrambling to halt the potential spread of a funguslike pathogen that kills oaks. In a nightmare come true, the pathogen, Phytophtora ramorum, was found this month in a nursery that has shipped potentially infected plants to more than 600 nurseries in 39 states. "We're dealing with a significant emergency," says Steve Lyle, a spokesperson for the California Department of Food and Agriculture (CDFA). As many as a dozen more nurseries in Southern California are probably infected.
The pathogen causes lethal trunk infections in several kinds of oaks, and it has killed tens of thousands in California. Many other species, including popular garden plants such as rhododendrons, can act as hosts. The disease has spread to 12 counties centered around San Francisco. In 2001, the U.S. Department of Agriculture (USDA) quarantined nurseries in those counties. Last year, however, a handful of nurseries in Oregon, Washington state, and British Columbia tested positive for the pathogen.
On 10 March, CDFA announced that an ongoing survey of 80 California nurseries has turned up P. ramorum at a 200-hectare facility run by a company called Monrovia, in Asuza, Los Angeles County. The pathogen had infected six varieties of camellias. These plants, as well as five other kinds of hosts, are now quarantined. Another nursery in San Diego County has also been confirmed positive and 11 more are likely infected as well, says Claude Knighten, a spokesperson for USDA, which has compiled a list of where Monrovia shipped host plants in the last 12 months.
State officials are now trying to track down those shipments. In Tennessee, agricultural inspectors have fanned out to take samples from host plants at two dozen garden centers on the list. "It's a huge undertaking," says Anni Self, a plant pathologist with the Tennessee Department of Agriculture. Nationwide, officials have contacted about 200 of the nurseries that received potentially infected material.
Scientists are also tweaking their plans for a survey of southeastern states, many of which have broad stands of susceptible oaks. Last year, USDA and state agencies conducted a pilot survey of P. ramorum in high-risk areas of seven states; they found no trace of the pathogen in nurseries or forests. This spring, they'll examine areas in 23 eastern states--and they're now focusing on areas that received shipments from Monrovia and any other infected suppliers. "Our goal is to sample around every one of these nurseries," says Steve Oak of the U.S. Forest Service in Asheville, North Carolina. "People are very concerned."