​Phytophthora ramorum

Af Hans Eiberg:

www.rhododendron.dk/sygdomme.htm

​Symptomer på Rhododendron:

Skud og knopper visner med en mørk misfarvning, som breder sig gennem bladstilken til bladet. Barken bliver mørk brun eller sort med tydelig overgang til sundt væv.Karakteristiske bladsymptomer er mørkfarvning, som breder fra bladstilk og/eller bladspids langs midtnerven i bladet. De visne blade hænger, men bliver siddende på grenen. Kviste og skud kan også visne uden bladsymptomer.

Af Klaus Hansen:

​Phytophthora ramorum er en meget agresiv svampesygdom, som er på vej fra Amerika.

Findes ikke i naturen i Danmark

I Danmark er Phytophthora ramorum endnu ikke et problem i naturen, fortæller Iben M. Thomsen, der er seniorrådgiver med speciale i træsygdomme ved Skov & Landskab på Københavns Universitet.

»Den er ikke fundet i skove eller andre naturområder i Danmark, så vidt jeg ved, men der har været enkelte tilfælde i haveanlæg og parker inden for de seneste år,« siger hun.

Hun mener, at det især er gået så galt i Storbritannien, fordi de har mange rhododendroner i den sydlige del af landet.

Et europæisk overvågningskrav betyder, at planteskolernes rhododendroner bliver tjekket for sygdommen, inden de plantes ud i Danmark og resten af EU.

Hvad skal du gøre, hvis du opdager visneskimmel

Hvis du som privatperson har Rhododendron eller andre planter med symptomer på visneskimmel, er bekæmpelsen simpel. Du skal blot fjerne de angrebne grene eller planter og smide dem i skraldespanden.

På den måde fjerner du plantedele, der kunne være angrebet af svampen.

​Hvad kan du gøre?

  • Hold øje med symptomer og værtplanter, så du hurtigt kan opdage et angreb
  • Fjern planter med større angreb og 15 cm af jorden under planterne eller dæk den med ukrudtsdug
  • Beskær i tørt vejr og med desinficeret værktøj
  • Fjern sygt plantemateriale uden risiko for spredning af smitte
  • Vær forsigtig ved håndtering af planter, fordi en såret plante er mere modtagelig for infektion
  • Undgå høj luftfugtighed omkring planterne, og udfør vanding om morgenen
  • Køb sunde planter, der er mærket med plantepas

Hvad gør NaturErhvervstyrelsen?

Vi overvåger for Phytophthora ramorum i planteskoler og havecentre samt i parker og lignende områder. NaturErhvervstyrelsen påbyder destruktion af de angrebne planter.

I planteskoler og havecentre skal modtagelige planter i en radius af to meter omkring angrebet også destrueres, mens planter, der står i en radius af ti meter omkring angrebet, bliver sat i karantæne i tre måneder.

Mere information?

Du kan finde mere information om overvågning for Phytophthora ramorum på vores hjemmeside:

www.naturerhverv.fvm.dk/overvaagning 

Her kan du finde information om mærkningskrav til planter og hvilke plantearter, der skal bære et plantepas som tegn på, at de er officielt kontrolleret: www.naturerhverv.fvm.dk/maerkningskrav 

Ministeriet for Fødevarer, Landbrug og Fiskeri

NaturErhvervstyrelsen

Planter og Landbrugslov

Nyropsgade 30, 1780 København V

Tlf: 3395 8000

planter@naturerhverv.dk, www.nature​rhverv.fvm.dk 

Værter i DK

Andre udvalgte værter i EU

Camellia*

Rhododendron*

Viburnum*

Chamaecyparis

Fagus sylvatica

Hamamelis virginiana

Ilex

Kalmia latifolia

Larix kaempferi*

Magnolia

Pieris*

Quercus*

Syringa vulgaris

Vaccinium ovatum

I UK er det gået værst ud over de med * markerede værter

November 2013

Blødende sår på bark af eg (Quercus) fremkaldt af Phytophthora ramorum

Kilde: Henrik Jørskov Hansen, Fødevarestyrelsen

Plantedirektoratet undersøger ikke enkeltplanter, da en laboratorieundersøgelse typisk koster flere gange plantens pris.

Om svampen:

Visneskimmel blev fundet i Tyskland og Holland i visnende grene af rhododendron i 1993. Efter omfattende studier blev svampen sidst i 2001 navngivet som en ny art med navnet Phytophthora ramorum. Umiddelbart ligner visneskimmel en række andre skadevoldere på rhododendron, men den adskiller sig fra disse andre svampe på forskellige punkter. Nogle af forskellighederne kan kun ses i mikroskop efter dyrkning af svampen. Det er karakteristisk for visneskimmel, at den i forhold til de lignende skadevoldere på rhododendron gror bedst ved forholdsvis lav temperatur (20°C) og at den gror langsomt. Visneskimmels gener adskiller sig på nogle punkter også fra de øvrige skadevoldere. Den forskel kan undersøges ved en PCR (Polymerase chain reaction) analyse

​Canadian Food Inspection Agency

Survey Map for Phytophthora ramorum, Québec 2008

​Map: Phytophthora ramorum Survey, Québec 2008

Date modified: 2009-11-22 

Phytophthora ramorum:

Gefährliche Pflanzenkrankheit erstmals in der Schweiz gefunden

Die Krankheit befällt vor allem Rhododendron- und Schneeballarten:

Rhododendron mit braunen Nekrosen auf dem Trieb.

Foto: Phytopathologie WSL

Charakteristisch für P. ramorum sind die grossen, abfallenden Sporangien (25-97µm). Sie werden in grosser Zahl auf Karotten-Agar gebildet. Darin entwickeln sich die Zoosporen, die aktiv in Wasserfilmen schwimmen und Pflanzen über Spaltöffnungen und Wunden.

Foto: B. Frey (WSL) 

Aus einer Baumschule stammt der erste Schweizer Nachweis der gefährlichen Pflanzenkrankeit Phytophthora ramorum, die in Kalifornien ein Eichensterben verursacht. Weil auch in Europa Schlimmes befürchtet werden muss, sind Quarantänemassnahmen unbedingt nötig.

Der erste Nachweis der gefährlichen Pflanzenkrankheit Phytophthora ramorum stammt vom September 2003. Der Erreger wurde in einer Baumschule des Mittellandes gefunden (Heiniger und Stadler 2003). Befallen waren lokal vermehrte Schneeball-Pflanzen (Viburnum bodnantense). P. ramorum ist ein Krankheitserreger, der erst kürzlich beschrieben wurde. Seine Herkunft ist unbekannt. Die meisten Infektionsherde in Europa sind auf wenige infizierte Baumschulen in den Niederlanden und in Deutschland zurückzuführen. Bis heute wurde diese Krankheit nur in Baumschulen, Gärten und Parks festgestellt. Betroffen sind vor allem Rhododendren- und Schneeballarten (Viburnum sp.). Weil sie im Westen Nordamerikas ein gefährliches Eichensterben verursacht, steht P. ramorum auf der Warnliste der Europäischen Pflanzenschutzorganisation (EPPO).

Die Verbreitungswege von P. ramorum sind noch nicht völlig geklärt. Auch über eine wirksame Bekämpfung der Krankheit mit Fungiziden liegen noch keine Erfahrungen vor. Der Krankheitserreger lässt sich nur nach Isolation anhand von morphologischen Merkmalen oder mit DNA-Analysen bestimmen.

Die Meldungen von weiteren befallenen Strauch- und Baumarten nehmen weltweit jedoch zu. In den USA wurde P. ramorum bis jetzt auf 19 Arten aus 11 Familien gefunden. In England wurde der Krankheitserreger bereits an Eichen und Buchen festgestellt, was zu grosser Besorgnis Anlass gibt (Tab. 1). Ob die europäischen Waldbaumarten gefährdet sind, ist zur Zeit noch ungewiss.

Massnahmen

Wer feststellt, dass eine Pflanze mit P. ramorum befallen ist, sollte folgende Massnahmen ergreifen:

  • Alle befallenen und alle anfälligen Pflanzen im Umkreis von 2 Metern von befallenen Pflanzen vernichten (Verbrennen, z. B. Kehrichtverbrennung). Bei Pflanzen in Containern die Erde und den Topf ebenfalls verbrennen. Die befallenen Pflanzen nicht kompostieren, da nicht sicher ist, dass P. ramorum beim Kompostieren abgetötet wird und die Gefahr besteht, dass die Krankheit später mit dem Kompost verschleppt wird.
  • Während zweier Jahre keine anfälligen Pflanzen in diese Quartiere setzten bzw. stellen.
  • Im Umkreis von 10 m von den befallenen Pflanzen alle anfälligen Pflanzen zurückbehalten. Auch für die restlichen Pflanzen der befallenen Partie gilt eine Verkaufssperre. Diese wird aufgehoben, wenn nach Feststellung des Befalls während dreier Monate aktiven Wachstums der Pflanzen kein weiterer Befall durch P. ramorum konstatiert wird.
  • Unbedingt vermeiden, dass Erde von befallenen Quartieren mit Schuhen und Werkzeugen verschleppt wird. Den Zutritt zu befallenen Quartieren beschränken.
  • Alle Wirtspflanzen von P. ramorum (Tab. 1) periodisch am Erzeugungsort bzw. in der Baumschule kontrollieren.

​Typisk svampeangreb: Se afsnit om desinfektion. Knive, sakse og save overfører let sygdomme.​

---------------------------------------

Phytophthora ramorum and Phytophthora kernoviae are strains of a deadly plant disease plaguing historic gardens, woodland and heathlands across England, Wales and parts of Scotland.

​​

According to environment minister Jane Kennedy, who today announced £25m for a five-year eradication programme in England and Wales, "if this disease spreads, it could mean parts of the countryside being cordoned off, and more limited public access - in addition to further loss of our precious woodland".

But eradication comes at a price, too. The main source of the disease is the Rhododendron ponticum which has invaded many large public gardens and historic estates. A cost-benefit analysis for the government last year [185k PDF] spelled out what is now going to happen. "Removal of plants may change the appearance of gardens to an extent where the public are deterred from visiting."​

Sabine Werres and Thomas Schröder

Reliable detection of a pathogen in nurseries requires good knowledge of the pathogen itself, epidemiology and disease development, and the different types of nursery management. Last, but not least, a well-trained staff with enough specialists is necessary for monitoring and survey.

Sampling

If the disease symptoms are not characteristic, samples must be taken to the laboratory for detailed analysis. The quality of the sampling method and the sample is as important for reliable monitoring and surveys as the specificity and sensitivity of the detection method.

​​

Important questions to consider include the following:

  • Where to take samples on a big field with seedlings, on a container stand, and so on?
  • Which part of the plant should be sampled?
  • How many samples must be taken?
  • When is the optimal season to take samples?

Of course, statistical rules can be used to calculate the optimal number of samples and to optimize the sampling procedure in the field. They are, of course, very helpful in determining where the pathogen is present in the field. To detect Phytophthora on plants, it is best to look at dips/depressions/swales in the field or at a container stand. In these dips the soil moisture is much higher and persists longer than in the surrounding area because the water accumulates there after rainy periods or after irrigation. And since P. ramorum (like all other Phytophthora species) needs water to develop and to infect, latently infected plants or disease symptoms will be first found in very moist places.

Which part of the plant should be sampled depends on the plant species. On Rhododendron, P. ramorum was detected from leaves and twigs. But experience with plant material from nurseries has shown that the detection rate can be higher from twigs than from leaves (Werres, unpublished data). That may be due to application of fungicides (see below). Concerning Viburnum, only samples from the stem base enable sufficient detection, not the wilting twigs. To summarize the experience with sampling in nurseries: If it is not certain whether the disease symptom really is caused by P. ramorum, it is always better to take the whole plant to the laboratory if possible, rather than just twigs or leaves.

It is very difficult to say how many samples must be collected for adequate monitoring, but it helps if samples are taken from different parts of the plant. Samples from different plants within a diseased area should be examined. The detection rate can be higher with younger than with old nursery plants, so more samples should be collected for monitoring old plants.

The best season for sampling in nurseries is late spring to autumn. Observations in nurseries have shown that, especially at high temperatures in combination with heavy rainfall, disease symptoms can occur within a few days after infection. Very often the assortment of plants in the nursery changes within a season. Therefore, more than one sampling date is needed within a season.

Detection methods

Detection methods for monitoring or surveys should be specific for P. ramorum, sensitive to detect latent infection, and robust toward influencing factors from the nurseries. In addition they should give rapid results and be easy to handle.

Initial diagnosis of P. ramorum infection in nurseries is usually based on disease symptoms. A reliable diagnosis by disease symptoms is possible only when:

  • the kind of symptom(s) that can develop is known;
  • the symptom itself is characteristic for the pathogen.

P. ramorum causes different symptoms depending on the plant species (see http://cemarin.ucdavis.edu/symptoms.html). Presently, disease symptoms caused by natural infection with P. ramorum in European nurseries are only known from Rhododendron, Viburnum, and in 2002 in United Kingdom two findings from Pieris and one finding from Camellia (http://www.defra.gov.uk/planth/publicat/sudden.pdf). Status on P. ramorum findings in Europe is available on http://www.eppo.org. Symptoms on other possible hosts in nurseries are mainly known from artificial inoculation of a single part of the plant. On Rhododendron, P. ramorum causes mainly a twig and shoot dieback (figure 1a, b). However, brown to black discoloration of single non-wooden twigs is characteristic not only for P. ramorum, but also for other Phytophthora species like P. citricola, P. cactorum, and P. syringae (figure 2a, b). So diagnosis solely by disease symptoms is not sufficient for P. ramorum. The wilting symptoms on Viburnum are very unspecific. To verify the diagnosis P. ramorum for this host, it is necessary to look for cambial necrosis at the stem base.

​​

1b

Figure 1: Twig dieback (a) and wilting (b) caused by Phytophthora ramorum

Figure 2a: Twig dieback on Rhododendron caused by Phytophthora cactorum

Figure 2b: Twig dieback on Rhododendron caused by Phytophthora citricola

Further detection methods for P. ramorum are discussed in detail on the Web site: http://cemarin.ucdavis.edu/symptoms.html. None of the methods show all criteria to be optimal. Based on the present knowledge from experiments in scientific laboratories and in laboratories of the plant protection services, combinations of different methods seem to be most effective.

Factors that can influence the detection rate

In many nurseries, specific fungicides are used for control of P. ramorum. Fungicides can suppress the development of disease symptoms, possibly leading to false-negative results and more difficult sampling. Furthermore, fungicides can influence the detection rate in plant or soil samples depending on the method used. For example, those methods that are based on the detection of living propagules, like baiting and microbiological techniques, will give false- negative results if the fungicide has damaged or killed P. ramorum. On the other hand, these methods can prove whether chemical control was successful. Residues of chemicals and/or ingredients can interact with the detection method itself so that false positive or false negative results are possible. Therefore, it is always very important to know the cultivation methods used in the commercial nurseries being monitored.

Monitoring

Monitoring of P. ramorum is done according to the definition of the IPPC Standard No. 6 (1997) for a "detection survey" (to conduct a survey in an area to determine if pests are present). A survey in this case is "an official procedure conducted over a defined period of time to determine the characteristics of a pest population or to determine which pest species occur in an area." In Europe, for example, the obligation to monitor the occurrence of P. ramorum is laid down in the EU-Directive 2002/757/EG (2002), so each of the EU member states has to provide data to the EU. Those data are also the background and the justification of regulatory measures for both import and export of host plants of the corresponding harmful organism.

The problems or preconditions for monitoring are described below. These apply not only to P. ramorum but also to all "new" harmful organisms.

At the beginning of monitoring in some cases, information on the biology of the organism is lacking so the following criteria have to be analyzed thoroughly to concentrate the usually limited amount of workers, laboratory capacity, and financial resources: confirmed host plants, potential host plants, risk areas, detection methods, and scientific data to develop a "survey plan." Of course, it is necessary to adapt monitoring according to new available information. For example, in Europe the monitoring of P. ramorum was first focused on Viburnum and Rhododendron species in nurseries, but now it has to be enlarged to public green areas. More data on potential host plants of P. ramorum are available as the result of artificial inoculation trials, so it has to be decided which plants should be included in the monitoring.

Monitoring usually is carried out concerning a new organism. Therefore, the results depend on the qualifications of the staff carrying out the monitoring. In summary, a well-trained staff, following good surveillance and record keeping practices is essential for effective monitoring.

References

Brasier, C.D., Rose, J., Kirk, S.A., and Webber, J.F. 2002.. Pathogenicity of Phytophthora ramorum isolates from North America and Europe to bark of European Fagaceae, American Quercus rubra and other forest trees. Proceedings of the Sudden Oak Death Symposium, Dec. 17.-18., 2002, Monterey, California. 30-31.

Proceedings of the Sudden Oak Death Symposium, Dec. 17.-18., 2002, Monterey, California. Session "Survey/Monitoring," 23-27, 88-93.

Phythophthora ramorum er særdeles alvorlig, her ses angreb på egetræer i Canada

Firma:

​Klaus Hansens planteskole

CVR: 60215553

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Mail:   klaus34hansen@gmail.com