Program Aid No. 1842

United States Department of Agriculture

Animal and Plant Health Inspection Service

Phytophthora

ramorum:

Stopping

the Spread

The U.S. Department of Agriculture (USDA) prohibits

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of race, color, national origin, age, disability, and where

applicable, sex, marital status, familial status, parental

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communication of program information (Braille, large print,

audiotape, etc.) should contact USDA’s TARGET Center at

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discrimination, write to USDA, Director, Office of Civil Rights,

1400 Independence Avenue, S.W., Washington, D.C. 20250–

9410, or call (800) 795–3272 (voice) or (202) 720–6382

(TDD). USDA is an equal opportunity provider and employer.

Cover photos [top to bottom]: An aerial view of Kent Lake,

CA, woodlands infected with the sudden oak death

pathogen, Phytophthora ramorum. The trunk of this infected

live oak exhibits bleeding cankers caused by P. ramorum

infection. Viburnum, a popular nursery shrub, is susceptible

to sudden oak death. (APHIS photo by R. Anson Eaglin.)

Federal and State cooperators survey for evidence of P.

ramorum nationwide. Camellias are also susceptible to P.

ramorum infection.

Photo credits: Captions indicate the source of all

photographs used in this leaflet. APHIS gratefully

acknowledges the cooperation of cited sources in furnishing

images for use in this publication.

Issued October 2005

Figure 8—Agricultural

officials survey for the

pathogen in areas

surrounding nurseries.

Here, leaf and branch

samples are collected

from a maple tree.

(APHIS photo by R.

Anson Eaglin.)

Nurseries in those three States that ship

P. ramorum host and associated host plants interstate must have their nursery stock inspected,

sampled, and tested by State officials before those

plants can be transported across State lines. APHIS

verifies the results of these tests. Nurseries that

ship nonhost plants interstate must undergo a

visual inspection to ensure that those plants are not

exhibiting P. ramorum symptoms before interstate

shipment.

Although quarantines are in place in 14 northern

California counties and 1 county in Oregon (where

the pathogen exists in the environment), eradication

of the pathogen from nurseries is the best defense

against long-distance spread. The goal of APHIS is

to determine the distribution of infected plant material in the United States and to limit the humancaused spread beyond the infected areas through

quarantines and a public education program.

APHIS is working with other Federal agencies,

the States, conservationists, and industry to accomplish this important goal. If you suspect that trees

or plants are infected with P. ramorum, contact your

State department of agriculture or your local extension specialist. To locate an extension specialist

near you, consult the blue pages of the telephone

book under “U.S. Department of Agriculture, Cooperative State Research, Education, and Extension

Service.” ■

Figure 6—Employees from the Maryland Department

of Agriculture’s Plant Protection and Weed Management

Division (left) and APHIS’ Plant Protection and Quarantine

program collect leaf samples from rhododendrons during a

national survey for P. ramorum in nurseries. (APHIS photo by

R. Anson Eaglin.)

most likely to experience P. ramorum damage and

then expanded the agency’s efforts to detect the

pathogen in the areas of greatest risk.

By the end of 2004, west coast nurseries had

shipped more than 2.3 million exposed or “at-risk”

plants to every State except Hawaii. Inspectors

found infected plants at 171 nurseries in 21 States.

Early in December 2004, APHIS began restricting the

movement of nursery stock from California, Oregon,

and Washington. At the time these restrictions

were established, these three States appeared to

present the greatest risk of moving P. ramorum in

nursery stock shipments.

Figure 7—An

APHIS plant health

safeguarding

specialist flags

sampled

rhododendrons for

destruction should

they prove positive

for P. ramorum.

(APHIS photo by R.

Anson Eaglin.)

Phytophthora

ramorum:

Stopping

the Spread
Plants Naturally Infected With

Phytophthora ramorum

Plants in the following genera are highly susceptible

to infection by P. ramorum: ■ Camellia, ■ Rhododendron, ■ Viburnum, ■ Pieris, ■ Syringa (lilac), ■ Kalmia (mountain laurel), ■ Quercus (oak), and ■ Umbellularia (California bay laurel).

To learn more about other plants susceptible to

P. ramorum, please visit the APHIS Web site at:

<http://www.aphis.usda.gov/ppq/ispm/pramorum>.

Symptoms caused by P. ramorum are difficult to differentiate from those caused by other pathogens.

For this reason, laboratory analysis is necessary to

confirm the presence of P. ramorum.

P. ramorum Makes Its Way Into the

U.S. Nursery System

During spring 2004, the California Department of

Food and Agriculture confirmed the presence of P.

ramorum, the sudden oak death pathogen, on several varieties of camellia plants at two large California wholesale production nurseries. Investigation of

shipping records revealed that these facilities had

shipped large quantities of several varieties of common household garden plants nationwide.

Figure 2—The trunk

of this P. ramoruminfected coast live

oak exhibits the

bleeding cankers

associated with

sudden oak death.

(Photo by Bruce

Moltzan, Missouri

Department of

Conservation, on

assignment.)

Figure 1—This aerial view shows tree death in Kent Lake, CA,

woodlands infested with the sudden oak death pathogen,

Phytophthora ramorum. (Photo supplied by the Oregon

Department of Agriculture and reproduced by permission.) ➚

Figure 3—Rhododendron, a common nursery plant, is one

of more than 70 plant species and cultivars susceptible to

P. ramorum. (Photo by Jennifer Parke, Oregon State

University; reproduced by permission.)

oaks, and Shreve oaks. The pathogen also infected,

but did not kill, a number of other plants.

Through extensive study and cooperative

research, scientists identified the pathogen in 2000

as a water mold called Phytophthora ramorum. It is

now known to be the cause of several plant diseases, including ramorum leaf blight, ramorum dieback, and Phytophthora canker diseases, but the

most widely known of these is sudden oak death.

First discovered in Germany and the Netherlands

in 1993, the pathogen has now turned up in 15

countries, including England, Belgium, Poland,

Spain, and the Canadian province of British

Columbia.

P. ramorum has a broad range of hosts, including

hardwoods (e.g., coast live oak), softwoods (e.g.,

coast redwood), landscape plants (e.g., camellia and

rhododendron), and herbaceous plants (e.g., western

starflower). To date, more than 75 plant species

and cultivars representing more than 45 genera can

either be infected by P. ramorum or facilitate its

spread.

Figure 4—These

camellia leaves show

P. ramorum-induced

leaf spot. (Photo by

Cheryl Blomquist,

California

Department of Agriculture;

reproduced by

permission.)

Figure 5—Nurseries can be a pathway for the spread of

Movement and Infection in Plants P. ramorum. (APHIS photo by Jim Writer.)

Phytophthora ramorum thrives in cool, wet climates,

but significant infections can occur in nurseries

with microclimates that favor disease. The organism is known to spread through wind-blown rain,

contaminated irrigation water, and infected plants,

and it may spread in ways not yet discovered.

Movement of the pathogen in soil or potting mix is

also possible.

Depending on the plant species, P. ramorum infections may occur on the trunk, branches, and/or

leaves. Infections that result in tissue death and

callus response on the woody portions of a tree are

referred to as cankers. In foliar and twig hosts,

symptoms can range from leaf spots to twig dieback, but these hosts rarely die from the infection.

Stopping the Spread

Immediately following that discovery, the Secretary

of Agriculture transferred to APHIS $15.5 million

from the USDA Commodity Credit Corporation to

prevent further spread of sudden oak death and to

detect and eradicate P. ramorum from nurseries that

had received the infected stock. APHIS launched

a massive program to track the shipments of

potentially infected host plants, test plants for

P. ramorum, destroy infected plant material, inform

nursery owners about disease management practices, and help nurseries and affected States recover

from this event. APHIS used computer-generated

models to predict which areas of the country were

Continued

n 1995, a mysterious and sometimes lethal plant

pathogen was detected for the first time in the

woodland environment of Marin County, CA. Over

the next several years, foresters, conservationists,

plant pathologists, and the general public noticed

that trees were dying in large numbers in coastal

northern California. Initially observed in a limited

number of oak species, the organism infected and

eventually killed thousands of tanoaks, as well as

coast live oaks, California black oaks, canyon live I

Background