^{WSU Puyallup} _{Ornamental Plant Pathology}

PPO Home > Academic Subjects > Agriculture > Irrigation / Water Management

Information for Master Gardeners

March 9, 2015 gary.maguire

Information for Master Gardeners

Sudden Oak Death

Sudden Oak Death is a disease caused by Phytophthora ramorum, an exotic microscopic organism that was accidentally introduced into the western US. The disease has killed thousands of trees in California and Oregon, and threatens natural environments in Washington.

Phytophthora ramorum also has a broad host range and presents a unique challenge to many industries in Washington. The effects on ornamental plant species are of particular concern. Therefore, we have prepared several resources to help you identify and report possible occurrences, included below.

Please contact us if you additional questions or concerns.

Sudden Oak Death Presentation Link — Click on the image above to download a PDF presentation about Sudden Oak Death

Symptoms of Disease

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.

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

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.

Rhododendron

Camellia

Viburnum

Additional Resources

Presentations

Websites

Brochures

Phytophthora ramorum: Stopping the Spread (APHIS)
Sudden Oak Death Program (WSU)
Monitoring Streams – Volunteer Information (WSU)
How to keep Phytophthora ramorum out of your Nursery (WSU)

Posters

Rhododendron plant at Bloedel Nature Reserve

YouTube Videos about Phytophthora

Water

March 9, 2015 gary.maguire

Water management for native plant nurseries

Many growers use water from an adjacent stream or river for irrigation. It is wise to treat this water before use, to prevent infection of crops with P. ramorum and other waterborne diseases.
Irrigating restoration plantings using stream water is risky if the plants are hosts and the water is contaminated. This is critical for Phytophthora spp. that cause root disease, such as P. lateralis and P. cinnamomi. While P. ramorum is not known to cause root disease, it can colonize the roots asymptomatically. The consequences of this is an area of research that needs further study.
Sediment deposited on plants after flooding is one means of transmitting P. ramorum inoculum from water to foliage.
A high water table will create a flooded situation in an in-ground planting, increasing plant stress and potential for Phytophthora infection. Back to Best Management Practices for Native Plant Nurseries

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

Pots

March 9, 2015 gary.maguire

Containers

Pots should not be in contact with the soil, as diseases can both leave and enter through drainage holes. Insulate pots from the soil surface using one or all of these methods: Gravel Weed cloth PalletTray
Fallen leaves and standing water + inoculum = Phytophthora infection
Do not use dirty pots, they may contain inoculum.
If you re-use pots, be sure to clean residual soil and sanitize, using a dilute disinfectant solution, hot water, or steam. Back to Best Management Practices for Native Plant Nurseries

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

Soil

March 9, 2015 gary.maguire

Soil and potting mix

This potting mix has been exposed to the elements and contains weeds and possibly diseases. It is important to store potting mixes in an area that is not in contact with the soil or where runoff water will infiltrate.

Cover the pile with a tarp or plastic to prevent contamination.

Or, even better, purchase clean potting soil from a reliable source.

Back to Native plant nursery BMPs

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

Symptom ID Guide

March 6, 2015 gary.maguire

Phytophthora ramorum Symptom ID Guide

Phytophthora ramorum

Plant Pathogen

Phytophthora ramorum is a microscopic organism that has evolved to parasitize plants. It is a particularly harmful plant pathogen because it can kill many of the species it can infect (hosts).

Biosecurity

Phytophthora ramorum is a global concern because it can infect many different plant species and spread relatively quickly. Unfortunately, it is challenge to manage because of its broad host range, long-term survival, and the variation in symptoms associated with infections. Furthermore, sometimes management practices (fungicides, biostimulants, etc.) can suppress the expression of symptoms, possibly resulting in the movement of an asymptomatic, but infected, plant.

More Information

More information about Phytophthora species and P. ramorum is available here.

Sudden Oak Death

General Information

Sudden Oak Death is a disease caused by Phytophthora ramorum. You can find more information about Sudden Oak Death at the links below:

Symptoms of Disease

Similar Symptoms

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

Phytophthora ramorum Symptoms

Rhododendron

Camellia

Viburnum

Other Online Symptom Guides

USDA Animal and Plant Health Inspection Service (APHIS)

Symptoms of P. ramorum (PDF Slideshow)
Ramorum foliar blight and dieback (PDF Slideshow)

California Oak Mortality Task Force (COMTF)

Forest Research (United Kingdom)

Identification and Symptoms of Ramorum disease

Forest Phytophthoras of the World

Phytophthora ramorum gallery

COMTF – Symptoms on Common Nursery Stock

Plant Disease Diagnostics

Guidelines for submitting a sample

Visit our Sample Submissions Guidelines webpage for information to help determine whether it will be helpful to submit a plant sample for professional diagnostics.

WSU Plant and Insect Diagnostic Laboratory

The WSU Plant Clinic can provide diagnostic services to identify the cause of symptoms on Rhododendrons and other plant species.

Click here to read their instructions for submitting a sample.

Puyallup Research and Extension Center Sign

Contact Us

Have more questions or concerns?

Contact us for more information or to schedule a site visit and Critical Control Point (CCP) Assessment. Fill out the webform on the right and we will reply shortly after.