January 2004 draft

Nursery Guide forDiseases ofPhytophthoraramorumon Ornamentals

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Diagnosis andManagement

Steven A.TjosvoldKarl R. Buermeyer

UC Cooperative Extension

Table of Contents

Introduction 1

Background 1

Biology 3

Symptoms on OnrnamentalNursery Hosts 4

Phytophthora ramorum inChristmas Tree Plantations 11

Quarantines and OfficialInspections 12

Nursery Inspection and Scouting 12

Sampling and Diagnosis 13

Disease Management 14

Acknowledgements 15

Resources 14

Susan FrankelUSDA Forest Service

Cheryl BlomquistCA Department of Food

and Agriculture

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• Avoid irrigation practices where the foliage is wetted. If sprinklers are used,irrigate in the morning to allow for thorough and quick drying of foliage.

• Monitor and maintain irrigation systems to insure the most uniform applicationof water to the crop. Correct low spots, areas of poor drainage, and clogged or leakingirrigation heads.

• Fungicides do not kill the fungus once an infection is established. Fungicidesmay help prevent infection. Consider applying appropriate fungicides to highly susceptiblehost crops when environmental conditions favor disease, such as in rainy winter andspring weather.

• Wounded leaves (even tiny wounds or scratches) are much more susceptible toinfection. Avoid handling host plants if they might be wounded when environmentalconditions favor disease.

• Avoid plant contact with soil, use raised benches, gravel or other means toelevate susceptible plants.

• Plants or plant parts that are suffering from poor vigor, disorders, or other seriousproblems should be removed from production areas and destroyed. A small number ofplants or plant parts could be bagged and disposed. If a cull pile is needed temporarily,the pile should be covered with a clear polyethylene sheet until the culls can bedestroyed or composted.

• Potting soil piles should be a minimum of 100 feet from susceptible hosts andcovered with clear polyethylene sheeting.

• Loading and delivery areas should be as far from production areas as possible.

AcknowledgementsThis publication has been funded in part by a grant from the US Forest Service, Stateand Private Forestry, Forest Health Protection.

The following people provided invaluable input into the preparation of thismanual:

Paul Beales, Central Science Laboratory, York, UKSusan Cohen, Solano Co. Agricultural Commissioner, Fairfield, CAKathy Kosta, CA Dept. of Food and Agriculture, Sacramento, CAAlan Inman, Central Science Laboratory, York, UKMerton Price, Santa Clara County Agriculture Commissioner’s Office, San Jose, CAGail Raabe, San Mateo Co. Agricultural Commissioner, Redwood City, CAAlexandra Schlenzig, Scottish Agricultural Science Agency, EdinburghKaren Suslow, Hines Nursery, Winters, CAPaul Tooley, USDA Foreign Disease-Weed Science Research Unit, Fort Detrick, MDSabine Werres, Federal Biological Research Centre for Agriculture and Forestry,

Braunschweig, Germany

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January 2004 draftIntroduction

Phytophthora ramorum, a newly discovered plant pathogen, has caused high oak mortality(Sudden Oak Death) and other diseases on wildland hosts in central coastal Californiaand southwestern Oregon. The pathogen also causes diseases on some ornamentalplants. In Europe, the pathogen has caused disease primarily on nursery crops, butrecently it has been tracked moving from infected nursery outplantings, to neighboringshrubs, and to lethal infection of adjacent native trees. This raises the concern thatinfected nursery crops could move the pathogen long distances to new areas and infectnew hosts. European isolates of the pathogen have been detected in nurseries in thePacific Northwest. In the United States, federal and state quarantines require inspectionof nursery stock for Phytophthoraramorum, and the pathogen is undereradication in Oregon and Canada.

In addition to providing a briefintroduction to the history and biologyof the organism, this guide containsphotos and descriptions of Phytophthoraramorum symptoms on ornamental plantsthat will aid in plant inspection andearly detection of the disease innurseries. Nursery managementpractices are suggested that will helpprevent the introduction anddevelopment of disease in nurseries.

Background

Disease occurrence on wildland hosts in the US- SuddenOak Death was first detected in the central Californiacoast in the mid to late 1990s. Tens of thousands oftanoaks (Lithocarpus densiflorus) and coast live oaks(Quercus agrifolia) have died. In Marin, Santa Cruz andMonterey Counties, portions of the wildland-urbaninterface forest changed dramatically: tree crownsseemed to turn brown in a few weeks, giving theimpression of intantaneous mortality.

In summer 2000, an unknown Phytophthora species wasisolated from the dying trees, proven to cause themortality, and recognized as the same as an unnamedPhytophthora species found on European nursery plantsin 1993.

As of winter 2004 Phytophthora ramorum has been detectedin wildlands in 12 counties in California and in CurryCo, southwestern Oregon (see map). Symptoms rangefrom lethal bark cankers on several oak species andtanoak to leaf spots and twig dieback on rhododendron.

Figure 1. Coast live oak mortality, Santa Cruz Co.,CA, 1999. Steve Tjosvold, UC Cooperative Extension

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1. ELISA (Enzyme-Linked Immunosorbent Assay, such as used in some field testskits) is used as a pre-screen to detect many species of Phytophthora. An ELISA testspecific to Phytophthora ramorum is not available;2. PCR (Polymerase Chain Reaction) uses DNA extracted from plant tissue orlaboratory cultures. In PCR, the size of the DNA band amplified from the unknownmust match exactly that from known Phytophthora ramorum DNA.;3. Selective culture media (such as PARP) can be used to isolate Phytophthoraramorum and other Phytophthora species from infected plant tissue. Plant tissue isselected from the leading edge of a canker or lesion and placed in selective media.Morphological characteristics of the mycelium, sporangia and chlamydospores can beused to aid in identification.

Disease Management

For most nurseries, the foremost objective of pest management programs is to preventthe introduction of the pathogen into the nursery via infected plant material. This canbe accomplished by careful inspection of new incoming host propagative material andstock and systematic and regular scouting of nursery stock to insure that the pathogenhas not been introduced (see Inspection and Scouting). Other practices that shouldbe helpful include:

• All nursery personnel need to be aware of the issues and disease symptomsregarding this pathogen and should be ready to alert the nursery scout or other authorityif characteristic symptoms are seen.

• Insure that incoming plant material coming from infested counties (the regulatedarea) has been properly inspected by agricultural inspectors.

• Infected leaves often drop from plants. For high-risk incoming shipments, offload the nursery stock in an area that can be cleaned of leafy debris. Sweep debrisfrom the receiving area and delivery truck and bag for disposal.

• Maintain good shipping and receiving records to facilitate trace-backs and trace-forwards if contaminated stock is detected.

For those nurseries surrounded by native host trees and shrubs and in an immediatearea where Phytophthora ramorum is found there are additional factors and practicesthat should be considered:

• Periodically inspect nearby native hosts for disease symptoms. Remove infectedhosts, especially California bay laurel, within 100 feet of the perimeter of nurseryblocks.

• Rain runoff coming down slope from areas containing infected hosts may containPhytophthora ramorum. Consider berms to prevent water and soil movement intoproduction areas from hillsides surrounding the nursery. Irrigation water pumped fromstreams and ponds in areas of infected native hosts may be contaminated withPhytophthora ramorum during winter and spring. Consider alternative irrigation sources,particularly in winter and spring.

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January 2004 draftA current list of more than 30 susceptible wildland and ornamental species can befound on the California Oak Mortality Task Force website: www.suddenoakdeath.org. Ithas been found in three forest types: California coastal evergreen forests, redwoodforests with tanoak understorys, and in Oregon in forests dominated by tanoak. A listof wildland species is contained in Table 1 below.

Table 1. Wildland plants known to be susceptible to Phytophthora ramorum inthe US (January 2004)

Plant Name Plant Part(s) Affected

Bigleaf maple (Acer macrophyllum) FoliarCalifornia bay laurel/pepperwood/Oregon myrtle Foliar & twig

(Umbellularia californica)California black oak (Quercus kelloggii) TrunkCalifornia buckeye (Aesculus californica) Foliar & twigCalifornia coffeeberry (Rhamnus californica) FoliarCalifornia hazelnut (Corylus cornuta) FoliarCalifornia honeysuckle (Lonicera hispidula) FoliarCanyon live oak (Quercus chrysolepis) TrunkCascara (Rhamnus purshiana) FoliarCoast live oak (Quercus agrifolia) TrunkCoast redwood (Sequoia sempervirens) Foliar & twigDouglas-fir (Pseudotsuga menziesii) TwigEvergreen huckleberry (Vaccinium ovatum) Foliar & twig/branchGrand fir (Abies grandis) TwigMadrone (Arbutus menziesii) Foliar & twig/branchManzanita (Arctostaphylos manzanita) FoliarPacific rhododendron (Rhododendron macrophyllum) Foliar & twig/branchPoison oak (Toxicodendron diversiloba) Twig/branchSalmonberry (Rubus spectabilis) FoliarShreve oak (Quercus parvula v. shrevei) TrunkTanoak (Lithocarpus densiflorus) Trunk/Foliar & twigToyon (Heteromeles arbutifolia) Foliar & twig/branchWestern starflower (Trientalis latifolia) Foliar

Disease occurrence on ornamentals in the US - In 2000, Phytophthora ramorum wasdetected on rhododendron plants in a Santa Cruz County nursery located in a nativeforest with many susceptible species and immediately surrounded by dead and dyingoak and tanoak trees. In 2003, Phytophthora ramorum was detected in several nurserieslocated in Santa Cruz County, the Bay Area, Central Valley, and Placer County inCalifornia; and in the Pacific Northwest in Oregon, Washington, and British Columbia.

Disease occurrence on ornamentals and native hosts in Europe - In 1993,rhododendrons and viburnums in Germany and the Netherlands showed twig dieback,cankers, and leaf spots. The unrecognized Phytophthora species isolated from theplants was largely ignored until 2000, when the morphologically similar organismassociated with oak and tanoak mortality in California was discovered.

In Europe, the pathogen has been found in over 400 nurseries and public gardens in 9countries on 13 genera, most on ornamental species covered in the next section. Untillate 2003, Phytophthora ramorum had only been found in plant nurseries and gardens,and not on native trees. However, beech, horse chestnut, and Holm oak in woodlandsettings have been found infected at multiple sites in England. These sites were

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Systematic inspection - Begin the inspection with an overview of the area from thecrop perimeter or with a quick walk-through. If suspicious symptoms are apparent,immediately examine them more closely to attempt to identify the problem. If nosymptoms are apparent, start by walking a systematic path through the crop. A commonscouting technique is to move relatively quickly down a walkway and scan both sides ofadjacent production beds, back and forth. If suspicious symptoms are seen, inspectplants more closely. A good-quality 10 X magnification hand lens can help identifymany pest or disease symptoms (although Phytophthora ramorum’s spores can not beseen at this magnification).

If plants are found with suspicious leaf spots or other symptoms, a sample should betaken (see Sampling) and the plant marked with plastic tape or a flag with the locationnoted on the scouting map. Also, a few plants can be selected at random to closelyinspect for early stages of lesion development. In these pots, the scout should look forinconspicuous leaf spots and fallen leaves with characteristic lesions.

Scouting can be prioritized to highest risk stock. Stock or cuttings of hosts from outsidesources should be monitored closely. Disease symptoms might take up to 4 weeks todevelop and until then plants may appear healthy. Note outside-source plants on scoutingmaps for weekly examination. Scouting should be intensified a few weeks after budbreak and especially in rainy spring periods when environmental conditions are highlyconducive to pathogen infection and development. For nurseries surrounded by nativehosts, scout areas immediately adjacent to these hosts, especially wet areas, nearpuddles, or rain runoff zones.

Practice good sanitation - Agricultural inspectors and other nursery visitors shoulduse caution to avoid moving contaminated plant material and soil between nurseries.Shoes, tools and vehicle tires should be thoroughly washed of soil and then sanitizedwith a disinfectant such as Lysol (R). Extra precaution should be taken when working inareas known to be infested; disposable overboots may be used and disposed of on site.

Sampling and DiagnosisSelect a fresh, representative sample of symptomatic plant parts including someassociated leaves and stems. The dry sample should be placed in a plastic bag andlabeled with date, genus, species, cultivar, and nursery location. The sample should bekept cool, away from direct sunlight, and delivered to the diagnostic laboratory within24 hours.

Send samples to your state’s plant pathology diagnostics laboratory, or contact yourlocal Agricultural Commissioner’s office.

The Federal quarantine requires submission of a minimum of 40 leaves whethersymptoms are apparent or not. Periodic sampling can confirm pest-free status and aidin early detection. Processing is a free service, provided by the state, that can build theconfidence of nursery customers.

Once the sample is received at the diagnostic laboratory there are three laboratorymethods that might be used to aid diagnosis:

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January 2004 draftassociated with previously identified infected rhododendron plantings. Infected redoaks, native to the eastern US, have been found in gardens in the Netherlands and theUK, also associated with infected rhododendrons.

Biology

Phytophthora ramorum, considered afungus, technically belongs in thekingdom Chromista (also known asstramenopiles), related to diatomsand brown algae. Phytophthoraspecies are Oomycetes or “watermolds” and require a moistenvironment to actively grow andreproduce. The genus Phytophthorahas over 60 species, many of whichare virulent plant pathogens. Thebody of the organism is made up ofthread-like strands, one strandcalled a hyphae, and collectivelycalled mycelium. Myceliumdevelops through leaf, bark, andvascular tissue.

Phytothphora ramorum produces severalreproductive structures important for pathogenspread and survival, including sporangia,zoospores and chlamydospores (see Figure 2).Sporangia contain zoospores, bi-flagellate sporesthat can swim in water. Chlamydospores areresistant, resting spores that help the pathogensurvive extreme temperatures, dryness and otherharsh conditions.

These spore structures commonly form on leafsurfaces of susceptible leaves and twigs followingprolonged wetting. They are transferred from plantto plant via windblown rain, in contaminated soilor via movement of live-infected plants. In forests,the pathogen sporulates prolifically on Californiabay laurel trees, (Umbellularia californica) whichserve as reservoirs for inoculum (Figure 3).

Figure 2. Hyphae, sporangia, and chlamydosporeson a leaf disk in laboratory medium. Jennifer Parke,Oregon State University

Figure 3. P. ramorum symptoms onCalifornia bay laurel leaves. SteveTjosvold, UC Cooperative Extension

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presence of infected host plants, and crop treeschecked for tip dieback. If in a generally infestedarea, removal of California bay laurel treeswithin 100 feet of the plantation edge mayminimize the risk of infection of growing stock.

Figure 19. Tip diebackcaused by P. ramorum ingrand fir Christmas treestock. Michelle Nachand,Santa Clara County Agricul-tural Commssioner’s Office

Quarantines and Official Inspections

Movement of Phytophthora ramorum hosts is regulated by California, Oregon, UnitedStates, Canada, the European Union, South Korea, Australia, and New Zealand. Thesequarantines define restricted plant parts and require annual inspections of nurseriesin infested areas, and pre-shipment inspections for host plants from infested countiesdestined for uninfested counties. Regulations are continually updated to reflect newfindings on Phytophthora ramorum’s host range and mode of spread. For completeinformation on regulations see the Regulations section of the California Oak MortalityTask Force website: www.suddenoakdeath.org, or consult your local county AgriculturalCommissioner’s office.

Nursery Inspection and Scouting

Systematic and careful inspection of nursery crops and propagative plant material isessential to prevent introduction of Phytophthora ramorum and limit its spread withinand from contaminated nurseries. The pathogen must be detected early, while at verylow levels. It may be like “trying to find a needle in a hay stack” but there are manysteps the nursery operator and agricultural inspector can take to make the job lessonerous. For this discussion, we will focus on detecting Phytophthora ramorum; a morecomprehensive scouting program is needed for general pest management.

A trained scout - A scout or inspector must be trained to recognize Phytophthora ramorumsymptoms and symptoms of other disorders that might mimic it. Designate one nurserystaff member as the scout and ask all employees to report unusual related conditionsor concerns to the scout.

Maps and Record keeping - A nursery layout map that includes the approximate locationsof targeted species is useful for the scout to get oriented and develop a strategy forscouting. A scouting map includes specie and cultivar names, locations, approximatequantity, and sources of targeted plants in scouted areas. During the scouting walk-through, record the scouting date, observations, and sampling information directlyonto the scouting map. The recorded information should be reviewed and used todevelop an efficient scouting strategy each time the nursery is scouted.

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January 2004 draftPhytophthora ramorum is heterothallic, meaning that sexual reproduction can only occurbetween two different mating types, called A1 and A2. The European Phytophthoraramorum population is predominantly A1 mating type, and the North American populationis A2. Oospores, the sexual spore, result from the union of A1 and A2 strains, but thisspore type has not been observed under natural conditions. However, the PacificNorthwest nursery infestations included the European population, A1 type, and in twonurseries both the North American, A2 and European A1 strains were found. Thisraises concerns that both mating types might eventually meet and reproduce sexuallyto create new, potentially more virulent hybrids, capable of exploiting new habitats andhost species.

Symptoms on Ornamental Nursery Hosts

Although hosts of Phytophthora ramorum show a range of symptoms, in general thedisease is characterized by irregular, necrotic leaf lesions, instead of distinct leafspots. A leaf infection can develop down the petiole into twigs. Sometimes infectionscan occur initially on or develop into stems and cause blights, where stem and associatedleaves wilt, become necrotic, and die. A distinct dark zone line can mark the advanceof the infection on some species such as California bay laurel. Under natural conditions,California bay laurel tends to be infected on the tip of the leaf, where the leaf hangsdown and water accumulates (see Figure 3, previous page). This characteristic can beseen in some nursery hosts as well.

Abiotic conditions that can look similar include sunscald, fertilizer burn or chemicalinjury, drought injury, freeze damage and root damage. The best way to distinguishabiotic damage from biotic damage is to check the underside and leaf margins. Forabiotic injury, margins of the lesions will be abrupt and distinct, not diffuse. (for example,compare Figure 4b, page 5 and Figure 6, page 6) Check for environmental problems,flooding, or openings in shade cloth, that may result in plant injury. Abiotic injury isoften uniformly distributed over the entire plant, while Phytophthora ramorum leaf spotsare often found on only a few leaves or one portion of the plant.

We present a detailed description of Phytophthora ramorum symptoms on ornamentalplants and Christmas tree stock. Native plant nurseries should use pictures anddescriptions of symptoms on native plants. See: Davidson, et al. 2003. Sudden oakdeath and associated diseases caused by Phytophthora ramorum. Online. Plant HealthProgress doi:10.1094/PHP-2003-0707-01-DG:http://www.suddenoakdeath.org/pdf/davidson2003.pdf

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Syringa (Oleaceae)

Symptoms on Syringa (lilac)include leaf lesions along theedges of leaves and the death ofleaf buds before opening, whichresults in the appearance of“dieback”

Cultivars found to be infectedinclude Syringa vulgaris ‘Belle deNancy’ and ‘KatherineHavermeyer’. There is noinformation available onresistant cultivars

Other diseases of lilac includebacterial shoot, stem and leafblight caused by Pseudomonassyringae. Bacterial blight affectsthe new succulent growth ofleaves and shoots of lilac in wetconditions. Infected new tissue turns soft and black, and infected leaves remain attachedto the stem. Ascochyta syringae blight affects shoots and flower stalks of lilac, but formsfruiting bodies which are visible with a hand lens, where no structures are visible onPhytophthora ramorum-infected tissue. Both bacterial and ascochyta blight can affectthe stems of lilacs, whereas Phytophthora ramorum primarily affects the leaves of lilac.

Figure 18. P. ramorum symptoms on lilac. AlexandraSchlenzig, Scottish Agricultural Science Agency

Other Hosts

Isolated instances of Phytophthora ramorum infections have also been found in othernursery stock in Europe. These include containerized yew (Taxus baccata) in the UK,causing leaf and stem dieback; strawberry tree (Arbutus unedo) in Spain, resemblingthe large leaf lesions on its Pacific coast-native relative, madrone (Arbutus menziesii);and lingonberry (Vaccininum vitus-idaea) with leaf spotting symptoms in a singleintercepted shipment of plants in Poland.

Phytophthora ramorum in Christmas tree plantations

Phytophthora ramorum can infect newly-expanding branch tips of Douglas-fir (Pseudotsugamenziesii) and grand fir (Abies grandis). Christmas trees plantations need to be inspectedand precautions taken to prevent the introduction and establishment of the pathogen.

To date, Douglas-fir and grand fir have only been found infected in locations wherethey are grown under heavily infested California bay laurel canopies. It appears thatclose proximity to California bay laurel or another source of inoculum is necessary forinfection of these coniferous species. Tree plantations should be inspected for the

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Figure 4. Phytophthora ramorumsymptoms on rhododendron. A & B:leaf lesions on R. ‘Todmorden’; C:stem and bud necrosis on a rhodo-dendron from Germany.

A

B

C

BBA, Germany

A & B Steve Tjosvold, UC Cooperative Extension

Symptoms of Phytophthora ramorum onrhododendrons include primarily leaflesions, although small branch dieback isobserved in Europe. Leaf lesions penetratethrough the leaf so the area of necrosis isidentical on both sides of the leaf. Lesionscan be triangular in shape and extend alongthe leaf mid-vein or located where water remains on the leaf for extended periods.Lesions are frequently seen along the edges, near the petiole and at the leaf tip.Lesion margins have diffuse edges which are most easily observed on the underside ofthe leaf. Small branch infections produce brown to black cankers. Leaves located distallyto the cankers can wilt, roll and eventually defoliate due to lack of water. Branchinfections can move distally or proximally, and through the petiole into the leaf base.This growth through the petiole results in the classic triangular-shaped lesion ofPhytophthora species.

Figure 5. Symptom pro-gression (approximately 3weeks) of a laboratoryinfected R. ‘Cunningham’sWhite’. (Aa & Ab) indicateinitial leaf infection sites.Infection Aa developsthrough petiole, formingstem canker (B). Infectiondevelops upward anddownward in stem, andinto leaf petioles andbases of leaves (C).Steve Tjosvold, UC Coopera-tive Extension

Rhododendron (Ericaceae)

Ab

B

C

Aa

Aa

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Kalmia (Ericaceae)

Note: The remaining plants have been found infected by Phytophthoraramorum only in the UK. They are included here because of the possibil-ity of the disease being transferred from another plant, or imported onplant stock.

Figure 16. Kalmia latifolia leaves infected with P. ramorum.Central Science Laboratory, DEFRA (UK) (Crown Copyright)

Symptoms on Kalmia (mountain laurel) have been found only on leaves. The disease ismanifested as necrosis along the leaf margins and down the midvein.

Kalmia latifolia is the only species to have been identified infected with P. ramorum.

Kalmia angustifolia has been shown in laboratory studies to be resistant to P. ramorum

Two other diseases known to cause leaf spotting in mountain laurel are Mycosphaerellacolorata which causes small silver to white spots, and Phomopsis kalmiae which causesround brown lesions with a distinct zone line, as opposed to the single amorphousnecrotic lesion shown in Figure 17.

Leucothoe (Oleaceae)

Figure 17. Leaf lesions caused by P.ramorum on leucothoe. Central ScienceLaboratory, DEFRA (UK) (Crown Copy-right)

Symptoms observed on leucothoe tend to begin atthe leaf tips. The pathogen subsequently growsthrough the leaf tissues towards the leaf base,causing a brown to black discoloration. No cankerson the stem have been observed.

The only cultivar found to be affected is Leucothoefontanesiana ‘Rainbow’, and no other cultivars havebeen tested for resistance.

Another disease that can cause leaf lesions inleucothoe is Cylindrocladium but unlike Phytophthoraramorum, it can girdle and kill stems.

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Azaleas have not been found infected with Phytopthora ramorum, but laboratory inocu-lation studies indicate that some azaleas, particularly deciduous azaleas, are suscep-tible (e.g., ‘Northern Hilights’ and California-native R. occidentale). Cultivars showingresistance include ‘Purple Splendor’ and ‘Hinocrimson’.

Other diseases and conditions that may cause leaf necrosis, and be confused withPhytophthora ramorum infection include other Phytopthora species that infect the aerialportion of rhododendrons, including P. cactorum, P. citricola, P. hibernalis. P. nicotianae(=P. parasitica) and P. syringae. Abiotic factors that can cause leaf necrosis includechemical injury, drought, cold, sun scald, and fertilizer burn (see Figure 6). Wiltingand death of an entire plant is more likely caused by root weevils or root-infectingPhytophthora species, not Phytophthora ramorum.

Figure 6. Leaf necrosis on rhodo-dendron leaves caused by un-known, non-infectious disorders.Steve Tjosvold, UC Cooperative Exten-sion

Figure 7. Rhododendron‘Vulcan’ showing symptoms ofboth P. ramorum and rust.Canadian Food InspectionAgency

Rhododendron species and cultivars found infected with Phytophthora ramorum

R. augustini R. 'Gomer Waterer'R. 'Baden Baden' R. macrophyllumR. balfourianum R. 'Mrs. G.W. Leak'R. brachycarpum R. 'Nancy Evans'R. catawbiense R. ponticumR. 'Catawbiense Boursalt' R. repensR. 'Catawbiense Grandiflorum' R. 'Roseum Elegans'R. caucasicum R. 'Schneewolk'R. 'Colonel Coen' R. 'Todmordon'R. 'Cunningham's White,' R. 'Unique'R. 'Everestianum' R. 'Vulcan’R. ferrugineum R. yakushimanum

Species resistant to Phytophthora ramorum in laboratory studies

R. arborescens R. minusR. carolinianum R. poukanenseR. macrosepalum R. simsiiR. maximus R. viscosum

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Viburnum (Caprifoliaceae)

Figure 14. P. ramorum stem (A) and leaf (B)lesions on Viburnum tinus. Cheryl Blomquist,CDFA

BA

Figure 15.Stem lesionin viburnumcaused by P.

ramorum.Central Sci-

ence Labora-tory, DEFRA(UK) (Crown

Copyright)

Symptoms of Phytophthora ramorum on viburnums includestem cankers and/or leaf necrosis. Stem cankers can occurat the base of the plant close to the soil line or on smallerbranches throughout the plant canopy. As a stem cankergrows, leaves normally attached to the stem in the cankerarea die and defoliate. As the stem becomes girdled by the canker, the leaves locatedbetween the canker and the stem tip wilt and eventually turn brown. These brownleaves usually stay attached to the stem. Leaf infections occur initially on the leaf tip,edge or petiole. A leaf infection can grow through the leaf, into the leaf petiole, andinto the stem to form a canker.

Other diseases or conditions - Frost damage can cause the blackening of young shootsand dieback Whole plants wilt due to drought, anaerobic conditions caused byoverwatering, or root diseases caused by Phytophthora species.

Viburnum species and cultivars found infected with Phytophthora ramorum

V. bodnatense V. fragrens V. plicatum V. ‘Schneewolke’V. x burkwoodii V. lantana V. plicatum tomentosum V. tinusV. davidii V. opulus V. pragnense V. utileV. ferreri

No information is available on resistant varieties

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January 2004 draftCamellia (Theaceae)

Figure 8. P. ramorum symptoms oncamellia Central Science Laboratory,DEFRA (UK) (Crown Copyright)

Figure 9. P. ramorum symptoms on Camelliasasanqua ‘Bonanza’ Cheryl Blomquist, CDFA

Figure 10. P. ramorum symptoms onCamellia japonica ‘Mrs.Charles Cobb’.Cheryl Bloomquist, CDFA

Figure 11.Infected C.

japonica‘Kumasaka’

CherylBlomquist,

CDFA

Symptoms of Phytophthora ramorum on camelliasare limited to leaf lesions which can vary in sizefrom a half a centimeter in diameter to coveringnearly half the leaf depending on environmentalconditions. Lesions are located primarily at theleaf tip or the edge of the leaf. Lesions can be surrounded by diffuse margins or thickblack zone lines. Infected leaves abscise prematurely, especially in Camellia sasanqua,where the lower part of the plant can defoliate. No tip dieback or small branch cankerscaused by Phytophthora ramorum has been observed on Camellia species.

Not many other diseases are likely to be confused with Phytophthora ramorum on camel-lias. Scorch symptoms are most commonly confused with Phytophthora ramorum infec-tion on certain specific camellia cultivars in areas that receive reflective heat and sunon the exposed leaves of the plant. Pestalotia and Pestalotiopsis can act as weak second-ary pathogens following leaf scorch and can cause necrosis.

Camellia species and cultivars found infected with Phytophthora ramorum

C. japonica 'Cleopatra' C. japonica 'Kumasaka' C. sasanqua 'Bonanza'C. japonica 'Jordan’s Pride' C. japonica 'Mrs. Charles Cobb C. sasanqua 'Jean May'C. japonica 'Joshua E. Youtz' C. japonica var. 'Silver Waves' C. sasanqua 'Setsugekka'C. japonica 'Kramer’s Supreme' C. sasanqua 'Showa-no-sakae'

No information is available on resistant species or cultivars

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Pieris (Ericaceae)

Figure 12. Branch tip diebackon Pieris japonica ‘Variegata’Jan Hedberg, Oregon Departmentof Agriculture

Figure 13. P. ramorum leaf (A) and stem (B) lesions on Pieris.Central Science Laboratory, DEFRA (UK) (Crown Copyright)

A B

Symptoms of Phytophthora ramorum on pieris (Andromeda) include necrotic leaf spotssimilar to those on camellias, as well as branch tip dieback.

Other diseases of pieris include aerial Phytophthora species that cause leaf lesionssimilar to Phytophthora ramorum. Phytophthora species also cause root rots (P. citricola, P.nicotianae (=P. parasitica) in pieris, but these are likely to affect the whole plant ratherthan individual leaves or twigs. Initial symptoms on new growth can resemble thatcaused by Botrytis.

Pieris species and cultivars found infected with Phytophthora ramorum

P. formosa var. forrestii P. japonica ‘Variegata’P. japonica ‘Flaming Silver’ P. japonica x formosa

The three Pieris japonica cultivars have been found infected with the A1 (European) matingtype in an Oregon nursery

No information is available on resistant species or cultivars

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