June 16, 2004 | By: Aimee Heald-Nielson

Since 1995, large numbers of oak trees in California’s coastal counties have been dying. Kentucky gardeners, landowners and foresters may wonder what that epidemic has to do with the bluegrass state.

“During recent years we’ve been concerned about the possibility that Sudden Oak Death disease would be found in Kentucky,” said John Hartman, Extension plant pathologist in the University of Kentucky College of Agriculture. “So far it has not been found here, but the threat is real because during the past year infected nursery stock may have been shipped to Kentucky and our gardeners need to be aware of the disease.”

Sudden Oak Death disease was confirmed in coastal California in 2000. The disease is caused by a fungus and its origin is unknown at this time. It has caused dieback of several oak species on the coast since 1995, and dozens of plant species are known to be susceptible to its invasion.

“The most common and lethal symptom of the disease on oaks is the formation of a moist canker in the bark on the trunk, which eventually girdles and kills the tree,” Hartman said. 

While mortality is mostly associated with oaks, other host species like Douglas-fir, rhododendron, California Bay laurel and camellia may show symptoms of leaf spots, leaf tip necrosis, blight and twig cankers, but not death. The latter plants serve as reservoirs for the Sudden Oak Death pathogen.

“The disease is favored by cool, moist conditions and according to the USDA Forest Service information, most of eastern Kentucky would be a high risk region for the disease because of favorable weather and susceptible hosts,” Hartman said. “In Kentucky, red oaks 
could become cankered and die, while rhododendrons, mountain laurel and others would be pathogen reservoirs.”

Hartman emphasized that so far the disease only has been found in California and Oregon forests and landscapes. Sudden Oak Death is spread through splashing and wind-blown rain, movement of the soil and on infected plant material. It can even be spread via hikers boots or equipment used in infected areas.

“Unfortunately, diseased camellias from a large California nursery were shipped to many states in the Eastern U.S., including Kentucky,” he said. “If the pathogen escapes into native oak forests, the effects could be catastrophic.

In response, officials from the USDA Animal and Plant Health Inspection Service are working with University of Kentucky to conduct a survey of Kentucky nurseries and forests to find and eradicate the disease if it is present.

“Kentucky gardeners need to be observant of, and bring to the attention of their county Extension agents, any unusual landscape plant disease outbreaks,” Hartman added. “Especially watch rhododendrons, camellias, viburnums and mountain laurels.


Writer: Aimee D. Heald 859-257-4736, ext. 267

Source: John Hartman 859-257-7445, ext. 80720