Sudden Oak Death Hits Texas

TEXAS - A newly described fungus has killed tens of thousands of oak trees and infected landscape plants along the northern California coast. Infected plants grown in California for the nursery industry have reached Texas nurseries - specifically Camellia japonica and Viburnum tinus, to date.

A quarantine restricting the movement of nursery stock from California growers to other states has been imposed by federal agriculture authorities. Under the U.S. Department of Agriculture quarantine, California nurseries are barred from shipping 59 plant species out of state until they can be declared free of the disease.

Landscape plants believed to be susceptible to the disease and commonly used in Dallas-area gardens include camellias, viburnums, pieris, European yew and azaleas. Fourteen states, not including Texas, have issued their own bans on host plants from California, and a few states have banned not only all plants from California but also soil, firewood and lumber, according to the California Department of Food & Agriculture.

Our heat can help

Dallas-based extension plant pathologist Dr. Kevin Ong says that, for the present, "the general public should not be overly concerned that the plant material they buy may be infected. To our knowledge, this pathogen does not fare well in hot conditions, such as our North Texas summers." Phytophthora ramorum, known as Sudden Oak Death, was first identified in 1995 in California. It has since spread from the state's northern coast, where most of the forest devastation has occurred, to Oregon and British Columbia and is transmitted to other locations by shipping infected nursery stock.

The fungus is a relative of the organism responsible for the 1845 Irish potato famine. It blemishes the leaves of plants it infects and kills some young plants. Infected plants have shown up in 12 states and 74 nurseries, including Texas, Louisiana, Florida and Georgia, according to the USDA. To date, plants shipped from Monrovia Growers in Azusa, Calif., and Specialty Plants in San Marcos, Calif., have tested positive for the fungus. The infected Texas plants were identified because Monrovia voluntarily traced shipments of its inventory to growers, and the plants were subsequently tested and destroyed.

The USDA announced it will spend $6.9 million on surveying the nation's plant nurseries. Inspectors with the agency's Animal and Plant Health Inspection Service and state plant health agencies will visit a representative sampling of nurseries and collect leaves for laboratory testing.

"It hasn't proved to be a problem in Texas, and we don't expect it to become one. California has been doing a lot of shipping to Texas for a long time," says Eddy Edmondson, president and CEO of the Texas Nursery and Landscape Association. "If we were gonna get it, we'd have gotten it long before now."

Texas Department of Agriculture entomologist Dr. Shashank Nilakhe advises that "TDA is assisting the U.S. Department of Agriculture in conducting inspections, issuing stop-sale orders and pulling samples for laboratory analysis."

He adds that "TDA is also checking nursery shipments at checkpoints to verify that plants from California are accompanied with appropriate certification and are free of the disease." Its personnel also are monitoring the situation to determine if a state quarantine against California plants is needed.

Because of the existing federal controls and state inspections and regulations, says Dr. Nilakhe, TDA does not believe such a measure is needed at this time.

Trying to identify the disease can be a problem without professional pathological testing. According to a USDA Forest Service report, leaf infections occur on some host plants, resulting in irregular lesions and twig dieback. In others, primarily trees, bleeding cankers develop on large branches and stems.

The cankers develop rapidly, can extend from ground level to as much as 5 feet up the trunk and ooze a dark reddish-brown liquid. Death follows soon after the appearance of the cankers.

Tricky identification

Identification of the disease from these symptoms, however, can be confusing because other plant and tree diseases can exhibit similar symptoms.

The USDA survey, in part, will try to determine if the more recently reported infestations occurred through artificial spread (as in infected nursery inventory) or spread naturally. "It's our belief Phytophthora ramorum is not going to survive here," says Mr. Edmondson. "The nursery industry is a $9 billion industry in Texas. We import probably 70 percent of our products sold here from other states. We don't want to jeopardize its economic impact, and we want to make sure the consumer is purchasing a clean product.

"As far as host plants and susceptible host plants," he continues, "I know of no evidence that the fungus is living here on its own or spreading."