Disease That Kills Oaks Is Found in Southland

A plant disease that has left large patches of oak woodland dead and brown on the North and Central coasts has been detected for the first time in Southern California.

State officials announced Wednesday that sudden oak death had been confirmed at a large L.A. County wholesale nursery that ships nationwide.

The discovery of infected camellia plants at Monrovia Nursery in Azusa, east of Los Angeles, marks a potential shift south for the disease.

Officials said it was too early to say whether the nursery find was an isolated incident or a sign of a broader spread to southern portions of the state.

“We’re still trying to get a sense of the scope of the infestation at the nursery,” said Steve Lyle, spokesman for the California Department of Food and Agriculture. “Until we know, it’s difficult to say what the implications are.”

Southern California is not considered a particularly hospitable place for the disease, which is caused by a fungus-like pathogen and seems to prefer moist, cool conditions.

“We’re fairly sure it’s not there at this point in natural areas,” said Katie Palmieri, information officer for the California Oak Mortality Task Force.

Noting that a primary means of transmission is splashing rainwater, Cato Fiksdal, Los Angeles County agricultural commissioner, said the disease would have a harder time spreading in southern regions of the state. “When you have tree touching tree in an oak forest, it’s easy to spread, but when you have individual oaks standing in a grassland, or species that are not susceptible interspersing them, it’s not so easy to spread.”

The disease has killed tens of thousands of oaks in 12 central and northern counties and is found on 40 tree and shrub species worldwide.

Many of the infected species, which include such common garden plants as camellias and rhododendrons, are weakened rather than killed by the pathogen.

It has proved the most lethal to several species of oak, including coast live oak, black oak and tanoak. All are found in Southern California.

Most of the California infections have been in wild lands, but the disease has also been found in a relatively small number of West Coast nurseries in California, Oregon, Washington and British Columbia.

In Europe, infected plants have been found in hundreds of nurseries.

The Monrovia discovery, confirmed by lab tests Monday, was made as part of a national nursery survey overseen by the U.S. Department of Agriculture.

Several varieties of camellia were found to be infected at the Monrovia Nursery, one of the largest and best known in California.

The company grows plants on hundreds of acres for shipment to other nurseries around the country.

“The primary concern at this point is that Monrovia has been shipping plants to other places,” said Fiksdal, adding that the company was “being very cooperative in making sure this doesn’t move.”

The infected plants will be destroyed and shipments are being traced. So far, one Washington state nursery that purchased plants from Monrovia has found infections.

Monrovia Nursery has stopped shipping all susceptible species and will inspect them before renewing shipments.

There is no treatment for sudden oak death in the wild, though last year the state approved the use of a pesticide that could slow or prevent infection on individual trees.

A federal quarantine is in place in affected northern and central counties but has not been imposed in Los Angeles County.

The regulations limit movement of infected material and require inspections of commercial operations to ensure that diseased plants are not moved out of infected areas.

A relative of the organism that wiped out Ireland’s potato crops in the 1800s, the disease turns leaves brown and produces oozing cankers that can lethally girdle a tree.

Other diseases can cause similar symptoms. “At this point, for the public to start going out and looking at their camellias may be a little premature,” Fiksdal said. “We will try to get information out.”

The California Oak Mortality Task Force maintains a website on the disease: www.suddenoakdeath.org