U.S. Trees Affected by Growing Number of Health Concerns

St. Paul, Minn. (November 30, 2004)—A number of emerging forest health issues are affecting the overall vitality of North American forests, say plant pathologists with The American Phytopathological Society (APS).

At a recent APS Northeastern Division meeting, plant pathologists highlighted several types of diseases that are of growing concern, including:

BUTTERNUT CANKER
First reported in Wisconsin in 1967, butternut canker is a fast moving, virulent disease that is killing butternut trees at a rapid rate throughout their range in North America. Butternut canker is caused by a fungus that infects the trees through wounds or natural openings in the bark. Infections kill the inner bark and create dark-colored, elongate cankers (dead patches) on woody tissues of exposed roots, stems, and branches. Infected trees are eventually killed due to multiple cankering that girdles the tree. In 2004, a survey of 1,384 permanently marked butternut trees in Vermont found that about 82 percent were diseased and that 41 percent had been killed. This level of mortality is about a 30 percent increase since the initial survey was completed in 1996. Forest pathologists at the University of Vermont have found that insects are involved in the dissemination of spores of the fungus. They are also using a Geographic Information System (GIS) to investigate geospatial patterns of disease development and tree mortality on the landscape.

SUDDEN OAK DEATH AND RELATED DISEASES
Since it was discovered in 1995, Sudden Oak Death (SOD) has killed tens of thousands of oaks in forests of California and Oregon. The fungus-like organism that causes SOD, Phytophthora ramorum, appears to be an exotic species that is not native to North America. The pathogen infects a large number of plant species, but mortality in forests is primarily restricted to oaks and tanoaks. While many of the non-oak plants do not die as a result of their exposure to the pathogen, they may help the disease to spread. Another tree that has recently been seriously harmed by a Phytophthora sp. in Northeastern U.S. is European Beech. The new beech disease is caused by a different species of Phytophthora, but plant pathologists say the disease has a number of similarities to SOD.

WHITE PINE BLISTER RUST
White pine blister rust, caused by the fungus Cronartium ribicola, has plagued white pines for more than 100 years. Although plant pathologists have developed methods to reduce the spread of this disease, research now indicates that the pathogen that causes this disease is moving into new areas and finding new hosts. White pine blister rust enters through needles and bark and forms cankers on the branches and trunks, eventually causing death. Rare pines in fragile ecosystems are now threatened by this disease.

Plant pathologists use a variety of methods to manage these and other tree diseases, but cite the need for further funding in order to develop additional methods of disease control. Critical forest disease research is conducted by plant pathologists in the U.S. Forest Service and at a number of universities.

APS is a nonprofit, professional scientific organization. The research of the organization’s 5,000 worldwide members advances the understanding of the science of plant pathology and its application to plant health.