Researchers work to halt spread of plant disease

Campus researchers are working with state officials to halt the introduction of Sudden Oak Death (SOD), a disease that affects more than 50 species of plants, including oaks, rhododendrons and camellias.

Last March, two California nurseries were found to have plants infected with Phytophthora ramorum, the pathogen that causes SOD. The nurseries shipped plants to more than 1,200 retail outlets throughout the U.S. and infected plants have been found in 12 states. In Massachusetts, more than 200 customers received mail order specimens from the infected nurseries.

Plant inspectors from U.S. Department of Agriculture and the Massachusetts Department of Agricultural Resources (MDAR) are collecting specimens from potential infection sites throughout the state, submitting samples to scientists at UMass Amherst for analysis. In addition, the state Department of Conservation and Recreation and the U.S. Forest Service are surveying natural areas in Massachusetts for signs of infection. In California, all nurseries that ship out-of-state must test negative for the SOD pathogen.

Robert Wick, a plant pathologist in the Microbiology Department, likens the destructive potential of SOD to that of chestnut blight that eliminated the American chestnut in the early 20th century. “American chestnuts were among the most dominant trees in the northeast U.S, but chestnut blight completely changed what our forests look like. If SOD were to become established, killing our oaks, our forests would change again.”

Wick suggests that one way to avoid SOD is to buy healthy plants from a reputable nursery or garden center. “The pathogen cannot spread far on its own: the most likely path of distribution is by shipping plants. The symptoms of SOD are a little tricky and may look like other disease problems,” says Wick. “People in the nursery trades have been alerted to look for the disease and they certainly don’t want this disease spread.”

Brad Mitchell of MDAR agrees. “Sudden Oak Death can be spread through infected plant material, rainwater or soil, but in order for it to become established in Massachusetts, someone has to bring it here. Our department is targeting retail nurseries in our survey to ensure that the disease is not being introduced via this route. Consumers need not avoid buying plants that are hosts for this disease, but should be careful not to buy diseased-looking plants.”

Sudden Oak Death was first found on rhododendrons in Germany and the Netherlands in 1993, and has been confirmed in dying trees, especially oaks, in California and on shrubs, including camellia and rhododendron in Oregon, Washington and British Columbia.