Sandra Fiser | 4/19/2005 10:29:00 PM
A relatively new disease of trees and ornamental plants has found its way into Louisiana, and officials are keeping watch to make sure it doesn’t spread.
One of those watching is LSU AgCenter plant pathologist Dr. Jeff Hoy, whose laboratory screened nursery plants from Louisiana retail nurseries for signs of Sudden Oak Death disease.
Hoy found the disease in plants from five retail nurseries that received wholesale plants from California, where the disease is believed to have originated. It was identified in camellias and viburnum plants that were shipped from one of the largest nurseries in the country.
The federal government has quarantined selected plants from California, and the Louisiana officials imposed a quarantine on all California nursery plants.
Hoy says the Louisiana Department of Agriculture and Forestry collected samples from plants with suspicious symptoms – dying leaves and dying growth tips – and sent the samples to his laboratory.
"We use very specific protocols," Hoy says. His laboratory uses two separate tests to look for the pathogen – known as "phytophthora ramorum." If both tests are positive, the samples are then sent to a national U.S. Department of Agriculture lab in Maryland to verify the diagnosis.
Hoy, who operates a pathology lab that serves Louisiana sugarcane growers, is familiar with testing for phytophthora. It’s common in agriculture.
"Phytophthora is a type of pathogen that’s responsible for a wide variety of important diseases in plants," Hoy says. "It generally lives in the soil."
Hoy tested plants from 20 nurseries, and five had infected plants, which were destroyed. The nurseries in question were all in the southern part of the state.
"Almost certainly infected plants have been sold, and there’s no way to trace them," the pathologist said.
Because the pathogen lives in the soil, it can be spread by splashing irrigation water or rainwater or through contaminated pots, tools, machinery and people’s clothes and shoes.
Hoy says the disease thrives in cool, wet conditions, so it won’t show up in the hot Louisiana summer.
"It may not be a problem under Louisiana conditions," he says, adding, "This may turn out to be a nursery problem and not a homeowner problem."
The LSU AgCenter plant pathologist says there are many potential hosts for the disease, and he points out that although it’s called Sudden Oak Death disease, it came to Louisiana on camellias.
The U.S. Forest Service has examined trees in Louisiana forests and not found any sign of the disease.
"Likely, this was the first introduction of the pathogen to Louisiana," Hoy says.
The plant pathologist also says no one really knows which plants may be susceptible to the disease. In fact, he’s not sure if the live oaks in Louisiana would be affected.
"Because of the many varieties of oak trees, some may be susceptible, and others may not," Hoy says.
Hoy says the disease is active on leaves at the junction of healthy tissue and damaged or dead tissue. He cautions, however, that the disease can’t be diagnosed by observing the symptoms. Lab tests are the only way to confirm its presence.
Unlike many other phytophthoras, Sudden Oak Death won’t necessarily kill the plants – despite its name, Hoy says.
Hoy’s involvement with Sudden Oak Death arose out of his expertise with phytophthora, according to Dr. Gerard Berggren, head of the LSU AgCenter’s Department of Plant Pathology.
"He had the lab and facilities to handle the diagnostics," Berggren said.
Hoy’s work was augmented by others in the South through the Southern Pest Detection Network, Berggren said.
"It was a team effort among several individuals and agencies who got together to expedite the process," he said.
Berggren said the LSU AgCenter’s Department of Plant Pathology has developed a plant disease diagnostic clinic to identify plant diseases throughout Louisiana.
"We’re currently in the process of hiring a diagnostician for the clinic, who’ll have the support of experts like Dr. Hoy for diagnoses," he said.