Sudden oak death (Phytophthora ramorium), first emerged as a serious problem in California. Discovered in 1995, the disease is known to have killed thousands of tan oak, coast live oak, and black oak - in 13 coastal counties of California and in Southern Oregon (USDA-Forest Service 1998; Fimrite 2004). New reports indicate that the disease has now spread to California buckeye (Garbelotto 2001) and maple, and to eight other states as well as Canada, the UK, and the Netherlands (Biever 2004, Garbelotto 2004). The disease appears similar to one discovered in Germany in 1993.

In the spring of 2004 a link was established between ornamental plants such as camellias, viburnums, and rhododendrons shipped from the Monrovia nurseries in California, and the spread of the sudden oak death fungus to garden centers across the nation (Associated Press 2004). The fungus has so far been found on nursery stock in a number of states including Washington, Florida, Georgia, North Carolina, Tennessee, Virginia, and Maryland, prompting a ban on the shipment of California nursery plants into a number of states (U.S. Department of Agriculture 2004). The fungus has also been discovered in British Columbia and in the U.K., again with suspected links to California shipments of ornamentals.

The discovery in July 2004 of the sudden oak fungus in a forest preserve in New York - the first discovery in any natural forest outside of California and Oregon - raise questions as to whether it is really the distribution of nursery stock that is causing the spread of the disease (Fimrite 2004). Subsequent tests of dead and dying trees have shown presence of the fungus in wild trees in Pennsylvania and in New Hampshire. Work is ongoing in an attempt to determine the extent and severity of the problem.

In mid-June 2004 it was announced that scientists had successfully sequenced the P. ramorium DNA, raising the possibility that a cure for the disease as well as better means of tracking it might be found. It is now known that the fungus invades plants through the bark and into the cambium layer, effectively cutting off the flow of food from the leaves to the roots. The fungus kills several species of oak and beech and can infect at least 40 other species, including a number of ornamental plants (Biever 2004).