Contained, but not eradicated

Transcription

1 Growing Knowledge Contained, but not eradicated The war against sudden oak death in southwest Oregon forests wages on, but nursery diligence still makes a difference By Ebba Peterson Twelve years ago, Phytophthora ramorum, a new species in the plant destroyer genus, was identified as causing the sudden death of oaks and tanoaks in the forests of California and southwest Oregon. This pathogen continues to spread within coastal forests. Although these forests are hundreds of miles from Oregon s nursery production areas, P. ramorum has also been shipped nationally by infested nurseries. This has caused great concern, given how damaging sudden oak death (SOD) is to native forests. Major impacts resulting from the disease include widespread death of tanoaks, a loss of wildlife habitat, and increased soil erosion. Landowners in SOD-stricken areas also face increased wildfire risk, hazards from falling large-sized trunks and branches, and the loss of important landscape and heritage trees. P. ramorum infects the leaves and roots of numerous plants, including those commonly grown in Oregon nurseries. These infections are easy to miss, especially since they do not kill the plants, and such a large number of species are susceptible. More than 100 plant species are on the host list. Shipment of these plants, especially infected Pieris, Rhododendron and Viburnum, has been implicated in the long-distance spread of P. ramorum Phytophthora ramorum causes two distinct sets of symptoms, depending on the host species. On certain members of the oak family, P. ramorum causes lethal bole (trunk) cankers resulting in the disease called sudden oak death. P. ramorum also causes foliar blight, as shown here, and shoot dieback on native plant species as well as many horticultural nursery crops. photo courtesy of usda/aphis throughout the West Coast. P. ramorum has also been shipped between Europe and the United States, and from the West Coast to other states where SOD has a good chance of establishing. The risk of P. ramorum moving outside its current range as a result of nursery trade has resulted in quarantines and certifications designed to prevent new outbreaks of SOD. Any nursery with a positive P. ramorum detection can attest to the cost of eradicating this pathogen. Preventing the shipment of infected nursery stock, therefore, must be a top priority in managing the spread of SOD. This becomes even An ongoing series provided by Oregon State University in collaboration with the United States Department of Agriculture and in partnership with OAN march 2014 DIGGER 33

2 Figure 1. The current extent of the sudden oak death (SOD) quarantine zone in southwestern Oregon, including new sites detected in Unlike in California, where SOD is quarantined by county, the Oregon SOD eradication program has allowed the Oregon Department of Agriculture to draw sub-county boundaries around areas of known infection. While eradication is no longer possible in most of the generally infested area, eradication is ongoing in the outer lying forests. MAP BY Alan Kanaskie, Oregon Department of Forestry 34 march 2014 DIGGER

3 contained, but not eradicated more important as SOD continues to expand within Oregon forests. Eradication and quarantine SOD is much more widely established in California than in Oregon. This is largely due to Oregon s eradication program, which combines the efforts of the Oregon Department of Forestry, USDA Forest Service, Bureau of Land Management, Oregon State University, and private industry partners. Several times a year, the program flies aerial surveys that attempt to identify dead or dying tanoak trees within the range of tanoak in Curry and Coos counties. These flights are combined with follow-up ground surveys and monitoring. When P. ramorum is detected, all major hosts in that location are cut and burned in order to destroy the pathogen and infected plant material. The eradication program has been able to eliminate the pathogen from some sites. Still, new infections have been found every year of the eradication program, most likely resulting from spread during the one- to two-year delay between infection and detection. P. ramorum disperses locally in rain splash and regionally in wind or fog, which also makes spread less predictable. Although the eradication program has not eliminated SOD from Oregon forests, it has slowed its rate of spread. Unlike California, where infested areas are quarantined by county, extensive surveying and control efforts in Oregon have allowed regulators to draw quarantine boundaries around sub-county regions of known infection. The quarantine boundary has expanded with the movement of SOD, predominantly to the north and east of the original infested areas. Originally confined to nine square miles, the quarantine boundary currently encompasses 264 square miles (still only 13 percent of Curry County). The Oregon Department of Forestry has recently suspended eradication efforts on non-federal land near the center of the quarantine area, as treatment delays DIGGER Marketplace Schurter Nursery Arborvitae Emerald green Virescens Boxwood Japanese Maples Otto Luyken Skip Laurel Various sizes & Varieties HOSTETLER FARM DRAINAGE Plastic Tubing 3"-24" Laser Grade Control Open Ditch for Buried Irrigation Plows and Trenches Pot-n-Pot Drainage Oldest Drainage Firm in Oregon Newest Subsurface Irrigation Techniques Canby, OR Materials and Technical Assistance Available Supplies for Small Growers SEED STARTING - Pots Trays Inserts Plug Trays Labels - large variety size, color & shape of blank plant pot & row markers Weed control, fertilizer, tapes & ties, watering, and more Enter coupon code DIGGER for a 15% discount for a limited time at AAAmercantile.com Your contribution today helps prepare the nursery industry leaders of tomorrow. OREGON NURSERIES FOUNDATION Contact the Oregon Association of Nurseries for more information or The ONF is a nonprofit 503(c)3 corporation. Donations may be tax-deductible; consult a qualified tax attorney or accountant. march 2014 DIGGER 35 DIGGER Marketplace

4 contained, but not eradicated in 2008 and 2009 resulted in infection over an area too large to treat with the available resources. This area is now a 56-square-mile zone called the generally infested area (GIA). Eradication treatments, which are most important for slowing disease spread, are now focused on new infested sites located at the outer periphery of the epidemic. Preventing further spread Preventing the re-introduction of P. ramorum (especially the other lineages, which were discussed by Niklaus Grünwald in the September 2011 issue of Digger) has been a crucial component of managing SOD in Oregon. P. ramorum was likely introduced into California and Oregon forests on nursery stock, before awareness of the pathogen was widespread. Regulations to prevent the further establishment of P. ramorum nationwide appear to be working. There has been no evidence of additional introductions to Oregon forests. Also, no new infections have occurred in native forests outside of Oregon and California. Still, trade in Oregon nursery stock has been harmed as a result of the perceived risk that infected plants pose to new areas. The costs to nurseries have included crop loss, increased sanitation requirements, a larger number of inspections, and other mitigation measures required by federal regulations wherever P. ramorum is detected. Production nurseries that are located in Curry County, but outside of quarantine boundaries, have experienced trade blockages and reduced business. Expenses and other problems associated with the spread of SOD will likely increase with the reduction in eradication efforts in southwest Oregon forests. In total, these costs are quite large and are shared throughout the nursery industry. A preliminary economic analysis performed in 2008 by Entrix Inc. for the Oregon Department of Agriculture (ODA) estimated costs to the Oregon nursery industry with and without eradication. Even assuming a slow rate of Figure 2. Pictured is a canyon infested by P. ramorum outside of the town of Brookings, Ore. Photos were taken in 2011 when only a few trees had died (top), and two years later in 2013 (bottom). Tanoak has a golden-colored crown, in comparison to the light green alders and dark green Douglas firs. Note the rapid progression of mortality in tanoak, for which sudden oak death gets its name. Such landscape-scale mortality is common in tanoak stands in California. It has only just been realized in areas in southwest Oregon, where eradication efforts have been suspended. Photos by Ebba Peterson 36 march 2014 DIGGER

5 spread if P. ramorum had not been controlled, SOD was expected to have cost the nursery industry around $65 million. Compared to the costs of the eradication program over the same time, $28 million, this program saved the nursery industry $37 million. DIGGER Marketplace Prevention the best tool As the SOD infestation expands, the chance that P. ramorum may be moved from the forest into the nurseries increases. This requires diligence on the part of nurseries to prevent Phytophthora from becoming established. Buyers need to have confidence that Oregon nurseries do not contain P. ramorum infected plants. This is vital for maintaining interstate trade. As with any non-native pest, prevention has proven to be the best management tool to control P. ramorum. In addition to best management practices, as endorsed by the ODA s Grower Assisted Inspection Program, new treatments are actively being assessed for their ability to manage Phytophthora persistence in nursery environments. These include methods for treating inoculum sources in water and soils, and foliar treatments to prevent infection and sporulation from key hosts. Managing P. ramorum has the added benefits of reducing the likelihood of establishment and movement of other Phytophthora species, many whose ecological and economical threats remain untested. DIGGER Marketplace Ebba Peterson is a post-doctoral scholar and instructor at Oregon State University. Contact her at petersoe@science.oregonstate.edu. For more information Visit the website for the California Oak Mortality Task Force. For details about P. ramorum in Oregon nurseries, visit the Oregon Department of Agriculture s P. ramorum information website at oregon.gov/oda/cid/plant_health/ Pages/sod_index.aspx. - Over 300 species grown from seed - Hard to find natives - Drought tolerant, high elevation - Quaking Aspen specialists - Highest Quality bareroot seedlings - Containers from 4-25 gallon Roots to grow on Phone: Fax: march 2014 DIGGER 37