The sudden oak death epidemic in Oregon

Authors: NAVARRO, SARAH - Oregon Department Of Forestry; LUJAN, MELISSA - Oregon Department Of Forestry; MCANINCH, GARY - Oregon Department Of Forestry; GOHEEN, ELLEN - Us Forest Service (FS); Grunwald, Niklaus - Nik; Larsen, Meredith; FIELAND, VALERIE - Oregon State University; TABIMA, JAVIER - Oregon State University; LEBOLDUS, JARED - Oregon State University

Submitted to: Digger
Publication Type: Trade Journal
Publication Acceptance Date: 8/15/2017
Publication Date: 9/13/2017
Citation: Navarro, S., Lujan, M.A., Mcaninch, G.L., Goheen, E., Grunwald, N.J., Larsen, M.M., Fieland, V., Tabima, J., Leboldus, J. 2017. The sudden oak death epidemic in Oregon. Digger. Available: http://www.diggermagazine.com/growing-knowledge-201709/.

Interpretive Summary: Oregon nurseries are increasingly threatened by the repeated expansion of the sudden oak death (SOD) epidemic in Curry county. Although this epidemic is geographically far away from the main nursery production areas, the continued expansion of the SOD quarantine area and the newly discovered introduced EU1 clone are distinct threats to the nursery industry. As SOD intensifies in SW Oregon, the likelihood of moving the pathogen from forest to nursery production areas is ever more likely.

Technical Abstract: SOD is a devastating disease killing oaks on the West Coast that is caused by a plant pathogen recently introduced into the US. This disease is caused by the fungal-like organism Phytophthora ramorum. Over 135 host plants, many of which are native to Oregon or common to Oregon's nursery trade, are hosts to P. ramorum. Scientists have documented 5 intercontinental migrations of P. ramorum and 3 distinct introductions into the North American west coast. Currently, we distinguish four clonal lineages named NA1, NA2, EU1 and EU2. The North American clone, NA1, was the first clone to arrive in the U.S. with plant imports of exotic ornamentals into nurseries and is responsible for SOD outbreaks in both California and SW Oregon forests. A second introduction, of the genetically distinct clone NA2, occurred into British Columbia and Washington nurseries. A third introduction of the European clone, EU1, likely arrived from Europe into Pacific Northwest nurseries. The origin of these clones is still a mystery but they most likely arrived in the US with live plant imports. It is clear that there is a direct link between forest and nursery production systems: the pathogen was initially introduced into nurseries and then subsequently moved into forests. The strategy addressing the spread of SOD in Oregon has transitioned from one of eradication to one of slowing disease spread. Despite faster spread in recent years, the disease is still limited to Curry County where forest activities such as timber harvest and the collection of special forest products have been affected in both previously infested SOD areas and areas within the quarantine. Additional required safeguarding measures during harvest operations, such as log washing and making sure soil and plant debris stay on site have had a large impact on timber harvest. If SOD spreads outside of the current quarantine boundaries, the next quarantine expansion would encompass all of Curry County. The implications of a larger SOD quarantine would further elevate economic losses and could include trade blockages and reduced business for Oregon growers. Impediments to the export of logs and lily bulbs from Curry County have recently been encountered. This risk to domestic and international trade could extend to other forest and agricultural commodities if the quarantine boundary increased.