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Symptoms of Phytopthora ramorum and look-alikes

Symptoms of Phytopthora ramorum and look-alikes

There are many diseases and pests that produce symptoms similar to those of Sudden Oak Death. This guide will help you to rule out SOD by identifying some of the more commonly encountered pest problems. In addition, it will help determine whether the plant is potentially infected with P. ramorum and the need for a sample to be collected.

On trees

Currently there are 5 tree species native to western North America that can be killed when they are infected with Phytophthora ramorum. These are tanoak (Lithocarpus densiflorus) and four oak species – Coast live oak (Quercus agrifolia), Canyon live oak (Q. chrysolepis), California black oak (Q. kelloggii), and Shreve oak (Q. parvula var. shrevei). In Europe, P. ramorum has been found to cause stem cankers leading to death of European beech (Fagus sylvatica), European sycamore (Acer pseudoplatanus), Horse chestnut (Aesculus hippocastanum), Northern red oak (Q. rubra), Sessile oak (Q. petraea), Southern beech (Nothofagus obliqua), Southern red oak (Q. falcata), and Turkey oak (Q. cerris). None of these tree species are native to Washington State, although they can be found planted as ornamentals. Some tree diseases that produce symptoms similar to P. ramorum are the following:

Armillaria root disease

Bacterial wetwood

Bleeding stem cankers

Phytophthora root disease and canker

On foliar hosts

Phytophthora ramorum produces leaf blotches, twig cankers, and shoot die-back on many plants. In some cases the shoot dieback may be severe enough to kill the plants (e.g., huckleberry and madrone), but in general they do not usually die as a result of P. ramorum infection. These are the most common hosts in Washington State. More will be added to the list as information becomes available.




Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center, 2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated January 2, 2013



Use new containers for high risk host plant material to prevent contamination of plants from potting media and plant debris that may contain pathogens. smIMG_5447
Store used containers that previously had host material separately from those planned for re-use. smIMG_5460
Used containers from host and high risk plants should be recycled if they are not going to be sanitized. Re-using these containers introduces the risk of infection from residual soil and potting media containing disease inoculum. smIMG_5458
Used pots can be steam sterilized for re-use. This steam cabinet was constructed from materials available at most hardware stores and can be scaled to any size needed.The length of exposure to steam depends on the number of pots being sterilized. smIMG_5472
A hot water bath is used to sanitize small containers. Pots are stacked inside the plastic bin, which is lowered into the hot water bath and held for several minutes. Length of time in the bath depends on the number of pots being sanitized. smIMG_5488Back to Managing Phytophthora diseases in the nursery

Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center, 2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated January 2, 2013

A Phytophthora tentaculata Pest Alert is now available!

A Phytophthora tentaculata Pest Alert is now available.  To date, P. tentaculata has been found infecting plants at three restoration sites – one in Monterey County and two in Alameda County.  It has not been found in the soil nor detected on adjacent native vegetation.  At the sites, the pathogen has been found on sticky monkey flower (Diplacus [=Mimulus]) and toyon (Heteromeles). Treatment, monitoring, and safeguarding at each location is ongoing to prevent spread.

Phytophthora tentaculata has also been found in five native plant nurseries to date in Butte, Monterey, Placer, and Santa Cruz Cos. on sticky monkey flower (Diplacus aurantiacus), toyon (Heteromeles arbutifolia), coffeeberry (Frangula californica), and Salvia mellifera. All infected plants were destroyed. Nearly 500 samples have been analyzed from native plant nurseries (voluntarily) as well as from additional restoration sites to test for pathogen presence.  In response to this situation, numerous native plant nurseries are now implementing best management practices, helping to insure that the best possible quality of plants are being grown. Surveys continue to determine if the pathogen occurs in undisturbed areas, particularly where the native plant nurseries have collected their propagative materials. These are the first detections of this Phytophthora in the US.  For more information, contact Kathy Kosta, CDFA, at

New Publications

Hansen, E.M. 2015. Phytophthora Species Emerging as Pathogens of Forest Trees. Current Forestry Reports. DOI: 10.1007/s40725-015-0007-7.

Species of Phytophthora are prominent in lists of emerging threats to forest ecosystems. We explore the conditions leading to and the consequences of the emergence of some Phytophthora species from their presumptive coevolved roles in undisturbed forest ecosystems to destructive agents as invasive forest pathogens. Phytophthora species are widespread, relatively abundant, very diverse, and poorly understood in many relatively undisturbed forest ecosystems. Three examples are examined in detail to illustrate the range of pathways to emergence and the varied consequences to forest environments. Phytophthora lateralis causes Port-Orford cedar root disease in western North America and now Europe. Phytophthora ramorum is causing unprecedented mortality in oak and tanoak forests in California, as the cause of sudden oak death, and is killing planted larch in the UK, and Phytophthora cinnamomi kills trees in parts of the world where it has been introduced. Active programs are underway in each case to manage, if not eliminate, their damage. In no case, however, has eradication been achieved. Prevention, by blocking initial introduction, has the highest probability of success.

Roy, B.A.; Alexander, H.M.; Davidson, J.; Campbell, F.T.; Burdon, J.J.; Sniezko, R.; and Brasier, C. 2014. Increasing Forest Loss Worldwide from Invasive Pests Requires New Trade Regulations. Frontiers in Ecology and the Environment. 12(8): 457–465.

Loss of forests due to non-native invasive pests (including insects, nematodes, and pathogens) is a global phenomenon with profound population, community, ecosystem, and economic impacts. We review the magnitude of pest-associated forest loss worldwide and discuss the major ecological and evolutionary causes and consequences of these invasions. After compiling and analyzing a dataset of pest invasions from 21 countries, we show that the number of forest pest invasions recorded for a given country has a significant positive relationship with trade (as indicated by gross domestic product) and is not associated with the amount of forested land within that country. We recommend revisions to existing international protocols for preventing pest entry and proliferation, including prohibiting shipments of non-essential plants and plant products unless quarantined. Because invasions often originate from taxa that are scientifically described only after their introduction, current phytosanitary regulations – which target specific, already named organisms – are ineffective.

Stream monitoring will be expanded in the Northern Olympic Peninsula, WA for Phytophthora ramorum

Northern Olympic Peninsula, WA Phytophthora ramorum stream monitoring will be expanded in spring 2015 in an effort to identify the source of inoculum contaminating the Dungeness River near Sequim, WA.  The river was found positive twice in 2013 and is not in the vicinity of a P. ramorum-positive nursery.  To date, follow-up sampling of streams in the area have not yielded information about the inoculum source.  The Chastagner lab at Washington State University, Puyallup will oversee the additional monitoring through a volunteer program and increase efforts to genotype isolates and DNA samples from waterways to help clarify the inoculum origin.  Several stormwater retention ponds in Pierce County will also be monitored to determine if landscaped areas in new developments may harbor the pathogen.

2014 National P. ramorum Early Detection Survey of Forests Summary

2014 National P. ramorum Early Detection Survey of Forests Summary – Along the West Coast, California, Oregon, and Washington conducted stream surveys using bottle of bait (BOB) and/or leaf baiting.  In CA, 146 sites were sampled over 5 baiting periods, with 19 positive samples collected (13 from previously positive locations).  Six of the positives were from watersheds that had not previously tested positive (See the January COMTF report for more information.).  In OR, 11 sites were sampled over 19 baiting periods, resulting in the detection of 6 positive waterways.  The OR survey samples were tested via culturing and PCR, with PCR diagnostics identifying 10 samples that were not found through culturing.  In WA, both BOB and leaf mesh bag sampling were used.  The two positive samples found were with the bait bag sampling method (not BOB) and from the same stream.

Four of the 9 participating eastern states had 9 P. ramorum-positive stream samples – AL (4), FL (1), MS (2), and NC (2).  Two of the positive streams (AL-1; FL-1) have not been previously positive and are each associated with a positive nursery.  Another Alabama positive stream has not been previously positive but is not associated with a positive nursery.  Plans for vegetation sampling near this stream are underway.

Bottle of bait (BOB – whole leaves and leaf pieces together in a bottle of collected water) monitoring protocols were adopted to detect P. ramorum for the forest stream survey in 2014.  BOB whole leaves detected five positive streams and leaf pieces detected four. Nine environmental plant samples from Georgia were tested for P. ramorum, but all were negative.  As found in previous years (2010-2013), the spring (March – May) bait period resulted in more positive samples (7) than the late season (October – November; 2). In total, 665 BOB samples were processed from 85 different sites in 9 eastern states (AL, FL, GA, MS, NC, NY, PA, SC, and TX).

BMP for Native Plant Growers

Best Management Practices for Native Plant Nurseries

CansMany of the plants that are grown in the PNW forest and native plant nurseries are hosts for P. ramorum. In addition to the economic impact that nurseries would suffer if P. ramorum was to be detected, the movement of infected plant material from these nurseries would likely result in the introduction of the pathogen into forest or natural sites. This may have significant economic and/or ecological impacts.

There are a number of phytosanitary measures that native plant nurseries can take to minimize the risk of inadvertently introducing P. ramorum or other Phytophthoras into a nursery site. Given the continued spread of P. ramorum inoculum from ornamental nurseries into nearby waterways, one of the keys is to treat any water that is used from streams or lakes for irrigation.

Another key is to be very careful about the plant material that is brought into the nursery and inspect new shipments closely for symptoms, especially if they are coming from an area where P. ramorum is established.

Native plants used in restoration sites are at risk for spreading P. ramorum into forests if they are infected. It is important to be aware of the source of irrigation water for these plantings.

Phytophthora and other diseases can spread in residual soil and plant material in pots that are re-used. Pots can be treated with disinfectants or heat to kill these organisms.

California Society for Ecological Restoration Quarterly Newsletter Summer Volume 26, Issue 2 has these two articles:

“Nursery Plants as a Pathway for Plant Pathogen Invasion” by Susan J. Frankel, Kathy Kosta, and Karen Suslow

“Solarization: A Simple and Low-Cost Method for Disinfesting Horticultural Containers” by Karen Suslow and Kathy Kosta

A Phytophthora tentaculata Pest Alert is now available. P. tentaculata is an emerging pathogen in California native plant nurseries and restoration plantings.

So far, P. ramorum has not escaped into the natural environment in the PNW except for in streams associated with positive nurseries and landscapes. Research on the amount of inoculum needed in water for infection, susceptibility and sporulation potential of plant hosts, and other topics will help us determine the level of risk to our forests. In the meantime, it pays to be cautious when working with host plants.

Photos of native plant nursery best (and worst) management practices

If you have ideas or photos to add to these pages, let Marianne know.

Thanks to Regina Johnson for many of the photos used in this section.

Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center, 2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated January 2, 2013

WA native plants

Pacific Northwest Plant Hosts

 026 smA laboratory study using detached leaves of some common broadleaf hosts found in the PNW was undertaken in summer of 2009 and 2010. Leaves were inoculated with a zoospore suspension of an NA1 isolate of P. ramorum and lesion area and infection frequency was evaluated. If P. ramorum was recovered from a leaf that did not show a visible lesion, it was considered to be infected asymptomatically. Sporulation potential of foliage of each plant species was also determined.

In general, the results of this study indicate that western Washington forests are not at high risk for damage caused by P. ramorum, based on the host plants tested. However, this is a subset of the many plant species that occur, and there may be a host species that is either extremely susceptible to infection or a prolific sporulator, that was not tested in this study. Plants posing the smallest risk of P. ramorum establishment were generally invasives and/or riparian species. The highest risk plants were commonly found in forested environments. These were fairly susceptible to infection and produced more chlamydospores than sporangia in their foliage.

Chlamydospore production was higher than sporangia production on many hosts in western Washington forests that were examined in this study. In other systems, such as bay laurel (Umbellularia californica) in California, and Rhododendron ponticum in the UK, P. ramorum outbreaks are driven by high concentrations of sporangia produced on foliage of these hosts. None of the Washington hosts tested produced as many sporangia as U. californica. Chlamydospores are a means by which P. ramorum can persist on a site in soil and decaying foliage, but will probably not produce large amounts of inoculum unless they germinate directly into sporangia, which can occur in flooded soils.

Back to Native Plants

Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center, 2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated January 2, 2013

For those who work with Native Plants

Native Plants

Learn about the possible risk of P. ramorum establishment on WA native plants and some invasives commonly found in WA forests and riparian areas.

Check out these best management practices used in ornamental nurseries.

More best management practices for native plant growers.

Multi-state research project: Are plant pathogens entering nurseries from wildland forests? Are native plant nurseries serving as pathogen gateways?


Phytophthora Diseases in Native Plant Production – Why Should I Care and What Can I Do About It? Marianne Elliott, College of Agricultural, Human, and Natural Resource Sciences, Washington State University, Puyallup, WA and Jennifer Parke, Oregon State University, Dept. of Crop and Soil Science & Dept. of Botany and Plant Pathology, Corvallis, OR. Presentation at 7th Western Native Plant Conference, December 6-8 2016, Vancouver WA.

Sudden Oak Death and other Phytophthora diseases in Washington ecosystems

Sudden Oak Death is devastating California forests, but what about in Washington? For those interested in the potential effects of P. ramorum on WA forests, native plants, and implications to trade in forest products. Other Phytophthora species and their role in forest ecosystems will be discussed.
Contact Marianne Elliott ( to schedule for your group.



A new Phytophthora disease of native plants in California.  Thomas D. Landis, Forest Nursery Notes – Summer 2015.

Sudden oak death and associated diseases caused by Phytophthora ramorum. Davidson, J. M., Werres, S., Garbelotto, M., Hansen, E. M., and Rizzo, D. M. 2003. Online. Plant Health Progress: doi:10.1094/PHP-2003-0707-01-DG.


Phytophthora species in native plant nursery stock: issues and implications – By Tedmund J. Swiecki and Elizabeth A. Bernhardt, Phytosphere Research, February 2017

Plant Associations in Washington’s Puget Trough Ecoregion WA Department of Natural Resources

A Phytophthora tentaculata Pest Alert is now available.

More about P. tentaculata in California:
Phytophthora tentaculata: History, Host Range, and Status in California Nurseries   (video)

Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center, 2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated January 2, 2013

FAQs about Sudden Oak Death

DSC01600 sm

Q:What is “Sudden Oak Death (SOD)”?

A: A new plant disease first detected in the U.S. in California in 1995. The disease attacks over 100 plant species in more than 37 different plant families. The disease got its common name (“Sudden Oak Death”) when thousands of healthy oak and tanoak trees in California appeared to suddenly die for reasons scientists couldn’t explain.

The cause of the disease is the water mold Phytophthora ramorum (commonly abbreviated as P. ramorum), which is a new species of Phytophthora that was described in 2001. Ramorum leaf and shoot blight is another common name for this disease on many of its hosts.

Q: How did SOD get to the U.S.?

A: We don’t know. Phytophthora ramorum is an invasive species of unknown origin.

Q: Is SOD a human health, pet health, or food safety issue?

A: No . P. ramorum only attacks some woody and herbaceous plants.

Q: How destructive is SOD?

A: It depends on the host plant attacked, and the strain of SOD involved. SOD is very lethal to certain types of oak trees –but damage on many plants is limited to dead spots on leaves and/or a twig dieback. You can learn more about SOD symptoms on some common host plants here.

Q: What could ultimately be the impact of SOD on Washington’s economy?

A: This is an important question. There have already been a number of economic impacts associated with the detection of this disease in Washington nurseries. Losses include the costs associated with the destruction of infected plant material and mitigation treatments (i.e. soil fumigation, etc.) as well as the lost opportunity to sell plants that are on hold during the Confirmed Nursery Protocol (CNP). Some nurseries have gone out of business, in part because of the costs of dealing with SOD. Some nurseries have also decided not to sell certain high risk host material, such as rhododendrons. Many of the high risk hosts are commonly used in landscapes and nurseries that do not carry these materials effectively face potential losses in sales. While the ecological impact on our forests associated with the spread of this pathogen from nurseries into the environment are unknown, it is clear that the resulting quarantines will likely have a major economic impact on the state. This will range from increased costs associated with monitoring and certification for nursery stock and Christmas trees, to the landscape industry, Christmas trees, the forest products industry, yard waste recycling programs, composting facilities, and regional ports.

Q: How many strains of P. ramorum have been identified?

A: A total of three strains have been identified; two North American strains and one European strain . All have been detected in Washington. You can learn more about the populations of P. ramorum in Washington here.

Q: How many times has SOD been detected in Washington since 2003?

A: Hundreds of times within 45 nurseries, two rivers, and several trace-forward landscape situations.

Q: Where have the detections occurred?

A: 1) Most detections have been made during “certification inspections” of Washington nurseries in the Puget Sound region.
2) A few detections have been made while testing for SOD in local rivers.
3) A small number of detections have been made during “trace forward” inspections of plants sold to individuals or landscape companies.

Q: What is a “certification inspection”?

A: An inspection of a nursery wishing to ship potential SOD host material out of state. Certification inspections are required by APHIS and are conducted by WSDA. A list of certified nurseries can be found on the WSDA website here. Nurseries that do not ship out of state are not on this list. When buying from a nursery, ask if they buy plants from certified SOD free nurseries or if they grow the material on site.

Q: What is a “trace forward” inspection?

A: An inspection of plants from a nursery where an infected plant was detected that have been purchased by a company or individual.

Q: Has SOD ever been detected on a plant shipped out of state from a Washington nursery?

A: Yes. On one occasion a nursery in South Carolina detected SOD on a plant shipped from Washington

Q: On what kinds of plants in Washington has SOD been found?

A: During certification inspections of nurseries, the five most common plants on which the pathogen has been found are 1) rhododendrons, 2) viburnum, 3) camellia, 4) kalmia, and 5) pieris. Outside Washington nurseries, the pathogen has been found only on salal.

Q: If I own one of these five plants and think the plant has SOD, what should I do?

A: First, take this quiz to determine the probability that your plant has SOD. If you suspect SOD, you can submit a sample to the WSU Puyallup Plant and Insect Diagnostic Laboratory.

Q: What other common plants are on the SOD host list?

A: Other host plants commonly found in Washington include salal, madrone, Oregon grape, and evergreen huckleberry. A complete list of SOD hosts can be found on the USDA-APHIS website here.

Q: How is SOD spread?

A: Primarily through physical contact of infected plants with other host plants. SOD is also spread through the movement of soil and water (i.e., rivers, rain, mist, dew, and splash from overhead irrigation) that has acquired the P. ramorum pathogen from prior contact with infected plants.