Phytophthora ramorum

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Phytophthora ramorum
Ulcer on an infected oak tree

Ulcer on an infected oak tree

Systematics
Department : Egg mushrooms (Oomycota)
Class : Oomycetes
Order : Peronosporales
Family : Peronosporaceae
Genre : Phytophthora
Type : Phytophthora ramorum
Scientific name
Phytophthora ramorum
Werres et al. 2001

Phytophthora ramorum is a kind of oomycete that as sudden oak death ( english sudden oak death - SOD ) known plant disease causes. The disease causes oak and other tree speciesto die; it has had a massive impact on oak populations in California and Oregon , but is also found in Europe . Symptoms are bleeding ulcers on the trunks of the trees and dying leaves , which in many cases lead to the death of the trees.

P. ramorum also infects a large number of other plant species, mainly ornamental shrubs such as rhododendron , viburnum and lavender heather , which causes symptoms on the leaves, called dieback ( English ramorum dieback, ramorum blight ). Such plants form the source of inoculation for new infections, since the pathogen- producing spores are spread via spray and rainwater .

P. ramorum was first described in 1995 and the origin of the pathogen in North America is still unclear, but the clearest evidence suggests that it was an introduced species there . There are very few regulatory mechanisms against the pathogen; only early detection and consequent elimination of the infected plants are helpful measures.

Occur

The disease is seen in the coastal regions of California between Big Sur (in Monterey County ) and southern Humboldt County . It is believed to occur in all coastal counties as well as in the immediately adjacent inland counties of this area, from Santa Clara County north to Lake County . P. ramorum has not yet been found east of the California Coast Ranges . There was evidence in 2001 in Curry County , Oregon , just north of the California border. The hardest hit was Sonoma County , where more than twice the area was infested as in all other counties.

At around the same time, a similar clinical picture was identified in continental Europe and the United Kingdom as being caused by Phytophthora ramorum .

Hosts and Symptoms

In North America

A hillside location in Big Sur, California, marked by "sudden oak death"

In California it was observed for the first time in 1995 that a large number of brown or tan areas ( English tanoak ) ( Lithocarpus densiflorus ) mysteriously died; this was ascribed to a species of the genus Phytophthora newly described in 2000 . The observation was eventually repeated in several other US states , as well as in the UK and Germany . It is assumed that the mushrooms were introduced with the seedlings or were previously undetected.

In ger areas , the disease can be recognized by the wilting of young shoots . Older leaves turn pale green, and after about two or three weeks the foliage will turn brown and cling to the branches. Dark brown fluid from the xylem can stain the bark of the lower trunk. The bark can break open and deposit resin that is visibly discolored. After the tree has died, root saplings try to sprout in the following year, but their tips soon curve and also die. Weevils ( Monarthrum scutellare ) have a high probability of colonizing the dying trees during midsummer and producing small heaps of fine white dust near the narrow boreholes. Later, bark beetles ( Pseudopityophthorus pubipennis ) penetrate and leave fine red dust as they drill. Small black cones, the fruiting bodies of mushrooms of the genus Hypoxylon, can also colonize the bark. The foliage can die more than a year after infection, even months after the beetles have entered.

In California holm oaks ( Quercus agrifolia ; English coast live oak ) and California black oaks ( Quercus kelloggii ), the first symptom is a burgundy-red to tar-black sap on the bark surface, which is often referred to as "bleeding tree cancer".

In addition to oaks, many other forest trees can host mushrooms; in fact, almost all woody plants in some California forests have been described as susceptible to P. ramorum in the United States , including rhododendrons, American strawberry tree ( Arbutus menziesii ), evergreen huckleberry ( Vaccinium ovatum ), California laurel ( Umbellularia californica ), California horse chestnut ( Aesculus ) , Oregon maple ( Acer macrophyllum ) Heteromeles arbutifolia , bearberry ( Arctostaphylos spp. ), coast redwood ( Sequoia sempervirens ), Douglas Fir ( Pseudotsuga menziesii ), buckthorn trees ( Rhamnus californica ), honeysuckle ( Lonicera hispidula ) and Quercus parvula ( English Shreve oak ). P. ramorum frequently causes a less severe disease in these hosts as "ramorum dying / Leaf bleach" ( English ramorum dieback / leaf blight occurs). Characteristic symptoms are dark spots on the foliage and, in some hosts, the death of shoots and branches. The disease kills some hosts like rhododendrons, but most survive. The progression of disease in these species is poorly documented. Sequoias develop discoloration on the needles and small ulcers on the branches, with purple lesions on the sprouts that can lead to their death.

In Europe

Dead leaves after infestation with P. ramorum

In Europe, Ramorum bleaching was first observed on rhododendrons and snowballs in the early 1990s, initially mainly on plants from containers in tree nurseries. The first symptoms were leaf and twig bleaching. By 2007 the disease had spread through tree nurseries and garden centers in 16 European countries; it has also been observed in gardens, parks and forests in at least eight countries. There was no significant endangerment of European oak species.

The pathogen was identified in 2009 as a cause of infection and death of numerous Japanese larches ( Larix kaempferi ) in Great Britain, namely in the English counties of Somerset , Devon and Cornwall . The infection of this species by Phytophthora ramorum was observed for the first time in the world . Since then, extensive populations of larch trees in Wales and south-west Scotland have been infested, prompting considerations about clearing large areas. The UK Forestry Commission noted that eradication of the disease was not possible and instead put in place a strategy to contain the disease and minimize its spread. Symptoms of the disease on larch trees are the death of the crown and branches, as well as pronounced yellowing or ginger-colored discoloration under the bark. In August 2010, diseased larch in the counties were Waterford and Tipperary in Ireland found. By February 2014, the disease had spread to larch plantations throughout the south of the country. Coillte, an Irish forest company that owns twenty infected woodlands, felled 16,000 trees in one of those forests after cutting 150 acres to contain the disease.

The closely related species Phytophthora kernoviae causes symptoms similar to P. ramorum , but infects beeches ( Fagus sylvatica ).

transmission

P. ramorum produces resting spores (chlamydospores) as well as zoospores , which enable movement in water with the help of flagella . P. ramorum is spread through the air; one of the main mechanisms of spread is by spraying water on other susceptible plants and by watercourses over long distances. Chlamydospores can withstand extreme conditions and are also able to hibernate. The pathogens benefit from injuries to the plants, which, however, are not essential for infection.

As mentioned above, not every P. ramorum- infested host dies . These plants are very important in the epidemiology of the disease because they act as an inoculum . In California, the California bay laurel ( Umbellularia californica ) appears to be the main inoculum. Garden waste such as leaves and root stumps are also able to serve as inoculum, since P. ramorum also survives saprotrophically . Because P. ramorum is able to infect many ornamental plants, the fungus can be transmitted through the exchange of these ornamental plants.

Hikers , mountain bike riders, horse riders and other people with various outdoor activities can unintentionally introduce the pathogen into areas ( hemerochoria ) where it was previously undetectable. After traversing infected areas, it can be helpful to clean shoes, tires, hooves, tools, camping equipment, etc. before returning home or traveling to non-infected areas, especially if there has been contact with muddy ground. In addition, the transport of firewood can bring sudden oak death to otherwise uninfected areas. Homeowners and travelers are encouraged to buy and burn locally produced firewood.

Two propagation strategies

Germ cells

P. ramorum is heterothallic with two mating types , A1 and A2, which are required for sexual reproduction. The European population reproduces predominantly after A1, while types A1 and A2 are found in North America. The genetics of the two populations show reproductive isolation. In general, the A1-type is more virulent than the A2-type, but there is more variation in pathogenicity in the A2 isolates. It is not currently clear whether the fungus reproduces sexually in nature; the genetic studies suggest that the lineages of the two reproductive types could be due to reproductive or geographical isolation and led to the observed evolutionary divergence.

Possible origins

P. ramorum is a recently described pathogen. There are various discussions about its origin and tribal evolution.

An introduced species

The evidence suggests that P. ramorum may be an introduced or introduced species; the occurrence of the European and North American populations is to be considered separately, as only one type of reproduction is observed on each of the continents - this is known as the founder effect . The differences between the two populations are then due to adaptations to the other climates. The evidence also includes the low genetic variability, as P. ramorum has not yet had time to diversify genetically since its introduction. The existing variability could be explained by multiple introductions with a few individuals who have adapted best to their respective environment. The behavior of the pathogen in California also suggests an introduction; It is believed that such a high mortality rate of the trees would have been noticed earlier if P. ramorum were an indigenous species .

Where P. ramorum originally came from remains unclear, but most researchers believe that Asia is the most likely, as most hosts of the species also come from there. Since different climates meet the requirements of P. ramorum , the most likely regions of origin are the southern Himalayas , Tibet or the province of Yunnan .

hybridization

In species of the genus Phytophthora , it has been shown that their evolution was driven by interspecific hybridization of two different species. When a species is introduced into a new environment , it causes episodic selection . The invading species encounters taxa present and could hybridize with them, creating a new species over time. If the hybrids are successful, they can compete with their parent species. According to this, P. ramorum would originally be a hybrid of two species. However, its unique morphology does not support this thesis. In addition, three genetic sequences (ITS, cox II and nad 5) were examined to establish a family tree of Phytophthora , but they were identical, so it can be assumed that P. ramorum emerged as a species only recently.

An autochthonous organism

P. ramorum could be indigenous to the United States. The infection rates may have been low at first, but environmental changes caused a change in the population structure . The alternative would be to confuse the symptoms of P. ramorum with those of other pathogens. When SOD first appeared in the United States, other pathogens and conditions were initially blamed before P. ramorum was found to be responsible. Likewise, among many other damaged plants in a forest, the likelihood of spotting a tree with SOD is low.

Ecological influences

In relation to humans, the loss of ger areas through the spread of the disease in culturally sensitive Native American settlements has been accompanied by the loss of acorns, which remain one of the most important traditional and religious foods in Northern California; they are used by the Yurok , Hoopa , Miwok and Karok . Similar effects arise with the decline of other autochthonous species in the ger area and oak forests, which are also traditionally used.

In forest ecology, the fungus contributes to the loss of ecosystem services caused by the loss of plant diversity and the animal species that depend on it.

In addition to the mortality caused by the disease, many indirect effects are expected. Various predictions of long-term effects are discussed in the scientific literature. While such predictions are necessarily speculative, indirect effects over shorter periods of time have been documented in some cases. One study showed, for example, that coastal redwoods ( Sequoia sempervirens ) grew faster after the neighboring ger areas were decimated by sudden oak death. Further investigations combined current observations and reconstruction or projection techniques in order to describe short-term effects, whereby future environmental conditions were also included. One study used this approach to investigate the effects of SOD on structural properties of sequoia forests.

Additional long-term effects of SOD could be inferred from regeneration patterns in areas where there were heavy losses. These patterns could indicate which tree species is replacing ger areas in contaminated areas. Such conclusions by analogy are important for forest types whose tree diversity was relatively low before the introduction of the SOD, e.g. B. Sequoia Forests. Until at least 2011, the only study on the comprehensive assessment of regeneration in SOD-infested sequoia forests showed no evidence that other deciduous tree species would immigrate. Instead, the sequoias populated most of the gaps. However, inadequate regeneration was also found in some areas; it was concluded that regeneration would continue. Since this study only looked at an area in Marin County (California), the results do not have to be transferable to other forests. Other impacts on local ecology include the high mortality in pollinator communities caused by the application of strong pesticides (agrifos). Beehives in the vicinity of areas heavily poisoned with Agrifos showed severe populations that were directly related to the application of the chemicals. In counties like Napa and Sonoma, indigenous pollinator populations can suffer severe damage due to the adoption of extensive rules on prophylactic pesticide application. Such damage to the pollinator populations, in turn, can have tertiary negative effects on the entire local plant community, which further aggravates the loss of biodiversity , which must be attributed to the SOD, and thus reduces the ecological value of the land.

Combat

early detection

Early detection of P. ramorum is essential for its control. Preventive counts are made on the basis of individual trees, which are more effective than overall considerations and depend on knowledge of the spread of the pathogen in the landscape in order to be able to estimate when it is approaching valuable trees. At the landscape level, the rapid and often invisible spread of P. ramorum means that any process that could slow its spread should be initiated at a very early stage of the infestation. Since the discovery of P. ramorum , researchers have been working on the development of early detection methods . These range from the diagnosis of individual infected plants to detection at the landscape level, which requires a large number of participants.

The detection of Phytophthora species requires laboratory tests. The traditional method is cultivation on a nutrient medium that does not support fungi (and in some cases no other Oomycetes such as Pythium species). The host material is obtained from the top of a plant that is infected with a tree canker caused by the pathogen; the obtained culture is examined microscopically to confirm the unique morphology of P. ramorum . Successful isolation of the pathogen often depends on the type of tissue removed from the host and the time of year.

Because of the complicated method, scientists have developed other approaches to identify P. ramorum . An ELISA test can be an initial non-cultivation test. However, it can only be a first test because it detects proteins that are found in all Phytophthora species. In other words, only the genus can be identified, not the species. ELISA tests can process large numbers of individual samples at the same time, so scientists use them to identify the likely infected plants when the number of samples is very large is. Some manufacturers produce small ELISA "field research kits" that homeowners can use to detect Phytophthora infection.

Researchers have also developed numerous molecular biological techniques for the determination of P. ramorum . This includes the replication of DNA sequences in the genome region of the internal transcribed spacer of P. ramorum (ITS polymerase chain reaction [ English polymerase chain reaction - PCR ] or ITS PCR); real-time PCR, in which the frequency of DNA is measured during the PCR and dyes such as SBYR green or TaqMan are used; a multiplex PCR which multiplies more than one DNA region simultaneously; and an SSCP , which uses the ITS DNA sequence from the PCR to differentiate the individual Phytophthora species based on the different speeds of diffusion through a gel.

Scientists have also started using properties of the DNA sequence to pinpoint the tiny differences between different isolates of P. ramorum . Two techniques suitable for this are AFLP , which enables the correct differentiation between the EU and US isolates by comparing the differences between different DNA fragments, and the investigation of microsatellites , which represent regions of the DNA sequence that are characterized by repeated base pairs . If propagules of P. ramorum enter a new geographic region and establish colonies, these microsatellites show in relatively short time mutations that occur gradually. Based on the microsatellite analysis of isolates from all over the state, researchers in California were able to construct trees ( graphs ) that make the spread of P. ramorum traceable from the two probable introduction sites in the counties of Marin and Santa Cruz into the state.

The early detection of P. ramorum at the landscape level begins with the observation of the symptoms on individual plants (and / or the discovery of brood bodies in watercourses; see below). Systematic soil- based monitoring in the distribution area of P. ramorum was impossible to establish due to the distribution of the infected trees over a mosaic of areas with complex ownership structures. In some areas, targeted ground-based investigations were carried out, for example in areas with high levels of recreational use or visitor density such as parks, at access points to hiking trails ( English trailheads ) or slipways. In California, the most successful strategy for ground-based infection detection is to observe symptoms on California bay leaves, as these are almost always associated with real oak and geraniums, the main “stepping stones” for fungal infections. In addition, P. ramorum can typically be discovered year-round in many (if not all) areas of California by laurel tissue cultivation techniques; this is not possible with most other hosts, including Oregon, where the ger areas are the most affected hosts.

As part of a nationwide program by the USDA, a ground-based survey to detect P. ramorum in 39 states was started from 2003 to 2006 to determine whether the pathogen has established itself outside the west coast region that has already been identified as infected. The test areas were classified using environmental variables required for the occurrence of the pathogen; their location in relation to possible sources of infection such as tree nurseries was also considered. The samples were obtained along transects whose points were in potentially infested forests or outside the vicinity of tree nurseries. The only positive samples were collected in California, so it could be assumed that no spread beyond the West Coast region has taken place to date.

Remote sensing has been shown to be helpful in detecting P. ramorum infections on large spatial scales, even if it does not allow for particularly "early" detection because it is dependent on the sighting of individual dead crowns in areas of ger from aircraft. A sophisticated GPS and mapping technology enables the explorers to mark the possible infestation sites and to have soil-based teams take samples of the vegetation.

The discovery of P. ramorum in watercourses was the first of the early detection methods . This technique uses pear or rhododendron branches as "bait" that are attached to ropes, bags, nets or similar structures. If plants in the catchment area are infected, there are likely zoospores of the pathogen (as well as other Phytophthora species) in adjacent watercourses. In suitable weather conditions, the zoospores are attracted to the “bait” and infect them; the induced lesions can be isolated and cultured, or the pathogen is analyzed using a PCR test. Using this method, P. ramorum was discovered in variously large, partly temporary catchment areas in California and Oregon, for example on the Garcia River (373 km²), the Chetco River (912 km²) and the South Fork Eel River (1784.5 km²). The method can detect the presence of infected plants before they pose a lethal threat. Of course, the exact location of the infected plants cannot be discovered - these can only be found by ground-based personnel.

A less technical approach to the discovery of P. ramorum on a landscape scale involves the landowners in the search. Many counties' agriculture departments and the offices of the University of California Cooperative Extension in California were able to document the spread of the pathogen in their regions through eyewitness reports and samples they brought with them. In 2008, the Garbelotto Laboratory at the University of California at Berkeley, together with local staff, hosted a series of training events known as "SOD Blitzes". These events were designed to provide local landowners with a basic understanding of P. ramorum and how to identify its symptoms; Each participant, who was equipped with a sampling kit, collected a number of samples from trees on their property and brought these samples to the laboratory for analysis. Hopefully this type of citizen science can help create a complete map of P. ramorum distribution in the workshop areas.

Wilderness Management

The methods used to manage P. ramorum depend on a number of factors, e.g. B. the spatial level on which the management should act. In Oregon, landscape and regional management was approached with a campaign for total eradication that took into account the different forms of ownership of infected forests; most of the forests were privately owned, but there were also some owned by the USDA Forest Service and the US Department of the Interior's Bureau of Land Management . The eradication campaign included consistent early detection through aircraft-based observation and water monitoring, a US Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS), and a quarantine led by the Oregon Department of Agriculture - Program to stop the spread of host material from areas where infected trees have been found, as well as promptly remove P. ramorum host vegetation , whether symptomatic or not, within 300 ft (91 m) of everyone infected tree.

Oregon eradication efforts, which began near the small town of Brookings in southwest Oregon in 2001, have been adjusted over the years in response to new findings about P. ramorum . For example, after inoculation experiments with different tree species it became clearer which hosts are susceptible to the pathogen; the executors therefore paid no further attention to non-host species such as Douglas firs and red alders . Another example was that after the knowledge that a small proportion of the ger area stumps on the host-cleared areas sprouted again and these sprouts were in turn infected - whether systemic or through re-infection from the environment is unknown, the actors began to do this Treat trees with small amounts of herbicides before felling to kill the root system. The effort has been successful in that, although the fungus has not yet completely disappeared from the Oregon forests, the epidemic has not been as explosive as it was in California.

In California, however, there are barriers to similar success in eradication efforts. On the one hand, the fungus is too well established in the forests of the Santa Cruz and San Francisco Bay areas to have been successfully eradicated since the time it was discovered. Even in relatively sparsely infested areas on the north coast and southern Big Sur, the institutions involved in management are faced with enormous challenges in terms of project management, coordination and funding. On the other hand, the management institutions seek to coordinate efforts between states, counties, and agencies, and to continue management in a more comprehensive manner.

Several options exist for landowners looking to limit the impact of the SOD on their properties. None of these guarantees the complete eradication of P. ramorum , none guarantees the protection of every tree from infection. Some are still in an initial test phase. However, if used carefully and thoroughly, some of the procedures increase the likelihood of either slowing the spread of the pathogen or limiting its effects on trees or tree populations. Suppose the owner had correctly identified the host trees and symptoms, turned the samples over to a local authority who would hand them over to an authorized laboratory, and received confirmation that the trees were infected - or, alternatively, the owner knows of nearby infected ones Trees and would like to protect his own stands - he can carry out a control attempt through measures of cultivation (for individual trees), silviculture (for stands) or chemical control.

The best evidence of that culture techniques in protecting the trees in front of P. ramorum are successful, comes from the research that has shown that there is a relationship between the risk of infection of stocks of the California oak ( Quercus agrifolia , English coast live oak ) and close to laurel stocks. In detail, it was found that laurel trees that grow within five meters of an oak trunk are the best indicators of disease risk. This suggests that the strategic removal of the laurel trees near California holm oaks reduces the risk of infection. Complete removal of the laurel trees would not be guaranteed as long as their proximity to the oaks appears to be the greatest risk factor. It is still unclear whether the same pattern applies to other oak species or ger areas. Research into ger areas has begun, but any management recommendations will be difficult to make because ger area branches also serve as inoculum for P. ramorum .

A promising approach for preventive infection control individual oaks and oaks Gerber - for the cure already infected stocks are not - is treatment with a phosphonate - fungicide , which is marketed under the trade name Agri-fos. Phosphonates are neutralized forms of phosphoric acid that do not act as direct antagonists of Phytophthora , but rather by stimulating various forms of immune reactions on the part of the trees. It is largely environmentally friendly if it is not applied to non-target plants and is applied either via an injection into the tree trunk or as a spray on it. If Agri-fos is used as a spray, it must be applied with an organic-silicate surfactant , Pentra-bark, in order to be able to adhere to the trunk long enough for the tree to absorb it. Agri-fos has proven to be very effective in preventive care, but must be applied as soon as there are visible symptoms of P. ramorum on trees in the immediate vicinity; if, on the other hand, the tree to be treated is already infected, no visible symptoms may yet appear (applies in particular to ger areas).

Attempts to take up control of P. ramorum using forestry methods began in 2006 in Humboldt County on the northwest coast of California. The trials took place on a variety of both private and public properties and generally focused on varying forms and degrees of landlord removal. The most extensive (50 acres (20 ha)) and most repeated attempts removed ger areas and laurel trees with chainsaws, with the shoots and seedlings as well as infected leaves being burned off on part of the areas. The hosts removed other approaches with modified "firebreaks in the undergrowth", in which all laurel trees, but not all ger areas, were removed; herbicides have been used to eliminate bay leaves and tanner areas; in addition, the laurel trees were only removed. The results of these procedures will continue to be monitored, but repeated sampling has revealed very low levels of P. ramorum in the soil and vegetation of the treated areas.

Management in nurseries

Research and development in the management of P. ramorum in nurseries ranges from the study of individual plants to research in the vicinity of the nursery to the spread of the pathogen across state and national borders.

A bouquet of studies have tested the preventive and curative effects of various chemical compounds on plants infected by P. ramorum , such as ornamental trees and Christmas trees. Many studies have focused on the four main hosts among the ornamental plants (rhododendrons, camellias , viburnum, and lavender heather). Several effective compounds have been found; the most effective include metalaxyl , dimethomorph, and fenamidon . In many of the studies, agreement was reached on the following: Chemical compounds are generally more effective for prevention than control; if used preventively, the treatment must be repeated at different intervals; and: chemical compounds can mask some symptoms and interfere with the verification of quarantine measures. In general, these compounds suppress , but do not kill , P. ramorum , and some researchers agree that repeated use could induce resistance in the pathogen. An overview of these studies can be found in Kliejunas (2007).

Another area of ​​research and developing practice deals with the elimination of P. ramorum from an infected environment of the nurseries in order to prevent the human-mediated spread via the trade routes of the ornamental plants. One way of doing this is through a robust quarantine and inspection program that the various federal and state authorities have implemented. The US Department of Agriculture's federal Animal and Plant Health Inspection Service (APHIS) program regulates nurseries in California, Oregon, and Washington; they must participate in an annual inspection regime; the nurseries in the 14 infested counties in coastal California and the limited infested area in Curry County, Oregon are required to undergo a more stringent inspection plan if they want to sell goods outside of their home territory.

Much of the research on the disinfection of tree nurseries has focused on voluntary compliance with “Best Management Practices” (BMP), with the help of which tree nurseries can prevent the introduction of P. ramorum as well as its spread from plant to plant. A group of tree nursery industry associations issued a list of BMPs in 2008 that includes chapters on prevention and management, training, internal / external monitoring / audits, recording / tracking and documentation. The document contains recommendations as specific as the avoidance of overhead irrigation on endangered plants; for the disinfection of plant reproduction containers, sorting areas, cutting benches, machines and tools after every crop rotation change in order to minimize the spread or introduction of the pathogen; and: the training of employees by suitable personnel or the documentation of self-training.

Research into the control of P. ramorum in tree nurseries has also focused on the disinfection of the irrigation water that contains the fungi or their spores. Irrigation water can be infected by laurel trees in the forests (if the source of the water is a stream), from laurel trees protruding over the irrigation reservoirs, from the runoff of infested forests or by regenerated irrigation water. Experiments in Germany with three different types of filters - slow filters , lava filters and plant-based sewage treatment systems - showed that the first two completely eliminated P. ramorum from the irrigation water , while 37% of the samples taken from the plant-based sewage treatment plants after the treatment still contained P. ramorum .

Because P. ramorum can persist in the soil indefinitely, programs to eliminate the pathogen in nurseries should also address its elimination from the soil. A number of chemicals have been tested for disinfecting floors, including: B. chloropicrin , metam-sodium , iodomethane and dazomet . Laboratory tests suggested that all of these chemicals were effective when placed in the bottoms of glass jars. In addition, a study in a volunteer tree nursery showed that fumigation with Dazomet (trade name Basamid) followed by a 14-day cover successfully removed P. ramorum from the soil. Other soil disinfection practices that are being investigated or of interest include sterilization , soil solarization, and paving of infected areas.

General hygiene in infected areas

One of the most important aspects in the control of P. ramorum concerns the prevention of the transmission of the pathogen by humans (hemerochoria). While enforceable quarantine regulations cover some of this aspect, cleaning up your own equipment from visitors or workers to infected areas is also important. In most cases, cleaning involves removing leaves and mud from potentially infectious surfaces - shoes, vehicles, and animals - before people leave the infested areas. The requirements to implement such practices become more complex as more people work in the infested areas, e.g. B. in construction, timber harvesting or fighting forest fires. The California Department of Forestry and Fire Protection and the USDA Forest Service have established guidelines and mitigation requirements for the latter two situations; Basic information on cleaning up P. ramorum- infested areas can be found on the California Oak Mortality Task Force website under “Treatment and Management” (under “Sanitation and Reducing Spread”).

Involvement of authorities

In England, the Forestry Commission, the Department for Environment, Food and Rural Affairs (DEFRA), the Food and Environment Research Agency , Cornwall County Council and Natural England have been working together since 2009 to record the infested areas and compile instructions for action. Natural England offers grants for rhododendron disposal through its Environmental Stewardship , Countryside Stewardship and Environmentally Sensitive Area programs . The Forestry Commission began clearing 10,000 acres (40 km²) of larch forests in south-west England in 2011 in an attempt to stop the disease from spreading. In Northern Ireland, the Department of Agriculture and Rural Development's Forest Service began cutting 14 hectares of infested larch stands in Moneyscalp on the border of Tollymore Forest Park in County Down in late 2011.

See also

Individual evidence

  1. ^ NJ Grünwald, M. Garbelotto, EM Goss, K. Heungens, S. Prospero: Emergence of the sudden oak death pathogen Phytophthora ramorum . In: Trends in Microbiology . 20, No. 3, 2012, pp. 131-138. doi : 10.1016 / j.tim.2011.12.006 . PMID 22326131 .
  2. ^ University of California Cooperative Extension: Sonoma County Sudden Oak Death Strategic Response Plan . Sonoma County and the Sonoma County Department of Emergency Services. February 2008. Retrieved April 10, 2019.
  3. ↑ a b c J. Parke: Sudden oak death, ramorum leaf blight, ramorum shoot blight . In: The Plant Health Instructor . 2008. doi : 10.1094 / PHI-I-2008-0227-01 .
  4. ↑ David M. Rizzo, Matteo Garbelotto, Jennifer M. Davidson, Garey W. Slaughter, Steven T. Koike: Phytophthora ramorum and Sudden Oak Death in California: I. Host Relationships . In: USDA Forest Service Gen. Tech. Rep. . PSW-GTR-184, 2002, pp. 733-740. Retrieved April 12, 2019.
  5. ↑ Sabine Werres, Rainer Marwitz, Willem A. Man In't veld, Arthur WAM De Cock, Peter JM Bonants, Marjanne De Weerdt, Karin Themann, Elena Ilieva, Robert P. Baayen: Phytophthora ramorum sp. nov., a new pathogen on Rhododendron and Viburnum . In: Mycological Research . 105, No. 10, 2001, pp. 1155-1165.
  6. ↑ a b Phytophthora ramorum . FERA. Retrieved February 17, 2014.
  7. ↑ a b Phytophthora ramorum . European and Mediterranean Plant Protection Organization. Retrieved February 17, 2014.
  8. ↑ UK Tree health recommendations aim to 'stop the spread , BBC News. May 20, 2013. Retrieved February 17, 2014. 
  9. ↑ a b c 'Unprecedented threat' for UK trees from pests , BBC News. September 3, 2012. Retrieved February 17, 2014. 
  10. ↑ Thousands of Afan Forest trees planted after infected larch , BBC. February 21, 2015. Accessed February 23, 2015. 
  11. ^ Richard Youle: Thousands of more infected larch trees to be felled . In: Wales online , June 21, 2018. 
  12. ^ Disease found in Japanese Larch Trees in Ireland , Department of Agriculture, Food & the Marine. August 17, 2010. Retrieved February 17, 2014. 
  13. ^ Barry Roche: Coillte urged to clarify the extent of larch disease in Gougane Barra , Irish Times. February 6, 2014. Retrieved November 22, 2016. 
  14. ^ Barry Roche: Cork's Gougane Barra Forest Park closing due to tree fungus , Irish Times. 4th January 2014. 
  15. ↑ Phytophthora ramorum and P. kernoviae . Royal Horticultural Society. Retrieved February 17, 2014.
  16. ↑ a b c d Jennifer M. Davidson, David M. Rizzo, Matteo Garbelotto, Steven A. Tjosvold, Garey W. Slaughter: Phytophthora ramorum and Sudden Oak Death in California: II. Transmission and Survival . In: USDA Forest Service (Ed.): Gen. Tech. Rep. . PSW-GTR-184, 2002.
  17. ↑ Anon: Phytophthora ramorum and Phytophthora kernoviae: Key findings from research . DEFRA, 2005.
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  19. ↑ a b T. J. Swiecki, EA Bernhardt: Increasing Distance from California Bay Laurel Reduces the risk and severity of Phytophthora ramorum Canker in Coast Live Oak . In: Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2007, pp. 181-194.
  20. ↑ Moving Firewood spreads Forest Pests . Retrieved October 24, 2011.
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  25. ↑ Clive Brasier, Joan Rose, Susan Kirk, Sandra Denman, Joan Webber: Comparative Host Range and Aggressiveness of Phytophthora ramorum and Phytophthora kernoviae sp. nov. on North American and European Trees . Retrieved April 15, 2019.
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  29. ^ FN Martin, PW Tooley: Phylogenetic relationships of Phytophthora ramorum , P. nemorosa and P. pseudosyringae , three species recovered from areas in California with sudden oak death . In: Mycological Research . 107, No. 12, 2003, pp. 1379-1391.
  30. ↑ H. Nicholls: Stopping the Rot . In: PLoS Biology . 2, No. 7, 2004, pp. 891-895.
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  34. ↑ Matteo Garbelotto, Pavel Svihra, David M. Rizzo: Sudden oak death syndrome fells three oak species . In: Californian Agriculture . 55, No. 1, 2001, pp. 9-19. Retrieved April 16, 2019.
  35. ↑ Tanoak - Notholithocarpus densiflorus . TreeGirl - intimacy with nature. Retrieved April 16, 2019.
  36. ^ Frederick V. Coville: Notes on the Plants used by the Klamath Indians of Oregon . Retrieved April 16, 2019.
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  38. ^ KM Waring, KL O'Hara: Redwood / tanoak stand development and response to tanoak mortality caused by Phytophthora ramorum . In: Forest Ecology and Management . 255, 2008, pp. 2650-2658.
  39. ↑ BS Ramage, KL O'Hara: Sudden oak death-induced tanoak mortality in coast redwood forests: Current and predicted impacts to stand structure . In: Forests . 1, 2010, pp. 114-130.
  40. ↑ BS Ramage, KL O'Hara, AB Forrestel: Forest transformation resulting from an exotic pathogen: regeneration and tanoak mortality in coast redwood stands affected by sudden oak death . In: Canadian Journal of Forest Research . 41, No. 4, 2011, pp. 763-772. doi : 10.1139 / x11-020 .
  41. ↑ a b M. Garbelotto, DJ Schmidt, TY Harnik: Phosphite Injections and Bark Application of Phosphite + Pentrabark Control Sudden Oak Death in Coast Live Oak . In: Arboriculture and Urban Forestry . 33, 2007, p. 8.
  42. ↑ a b c d J. T. Kliejunas: Identification and Distribution . In: California Oak Mortality Task Force (ed.): Sudden Oak Death and Phytophthora ramorum: A Summary of the Literature 2007.
  43. ^ S. Mascheretti, PJP Croucher, A. Vettraino, S. Prospero, M. Garbelotto: Reconstruction of the Sudden Oak Death epidemic in California through microsatellite analysis of the pathogen Phytophthora ramorum . In: Molecular Ecology . 17, No. 11, 2008, pp. 2755-2768. doi : 10.1111 / j.1365-294x.2008.03773.x .
  44. ↑ JM Davidson, CG Shaw: Pathways of Movement for Phytophthora ramorum, the Causal Agent of Sudden Oak Death  (= Sudden Oak Death Online Symposium). The American Phytopathological Society, 2003.
  45. ^ PE Maloney, SC Lynch, SF Kane, CE Jensen, DM Rizzo: Establishment of an Emerging Generalist Pathogen in Redwood Forest Communities . In: Journal of Ecology . 93, No. 5, 2005. doi : 10.1111 / j.1365-2745.2005.01031.x .
  46. ↑ E. Goheen, USDA Forest Service, personal communication
  47. ↑ SW Oak, AH Elledge, EK Yockey, WD Smith, BM Tkacz: Phytophthora ramorum Early Detection Surveys for Forests in the United States, 2003-2006 . In: Proceedings of the Sudden Oak Death Science Symposium . USDA Forest Service, Santa Rosa, CA, pp. 413-416, (Accessed April 17, 2019).
  48. ^ JA Mai, W. Mark, L. Fischer, A. Jirka: Aerial and Ground Surveys for Mapping the Distribution of Phytophthora ramorum in California . In: Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our Knowledge . USDA Forest Service, Monterey, CA 2006, pp. 345-360.
  49. ↑ SK Murphy, C. Lee, J. Bienapfl, Y. Valachovic, DM Rizzo: Monitoring Phytophthora ramorum Distribution in Streams within Coastal California Watersheds . In: Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our Knowledge . USDA Forest Service, Monterey, CA 2006, p. 531.
  50. ^ SK Murphy, C. Lee, Y. Valachovic, J. Bienapfl, W. Mark, A. Jirka, DR Owen, T. Smith: Monitoring Phytophthora ramorum Distribution in Streams within Coastal California Watersheds . In: Proceedings of the Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2008, pp. 409-411.
  51. ↑ EM Goheen, EM Hansen, A. Kanaskie, MG McWilliams, N. Osterbauer, W. Sutton: Eradication of Sudden Oak Death in Oregon . In: Phytopathology . 92, 2002.
  52. ↑ EM Goheen, EM Hansen, A. Kanaskie, MG McWilliams, N. Osterbauer, W. Sutton, L. Rehms: An Eradication Strategy for Phytophthora ramorum in Oregon Forests . In: Phytopathology . 94, 2004.
  53. ↑ A. Kanaskie, N. Osterbauer, M. McWilliams, E. Goheen, E. Hansen, W. Sutton: Eradication of Phytophthora ramorum in Oregon Forests - Status after Three Years . In: Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our Knowledge . USDA Forest Service, Monterey, CA 2006, pp. 489-490.
  54. ^ YC Valachovic, Lee J. Marshall, H. Scanlon: Wildland Management of Phytophthora ramorum in Northern California Forests . In: Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2008, pp. 305-312.
  55. ↑ JT Kliejunas: Management and Control . In: Sudden Oak Death and Phytophthora ramorum: A Summary of the Literature . California Oak Mortality Task Force, 2007.
  56. ↑ USDA APHIS (ed.): Phytophthora ramorum; Quarantine and Regulations  (= 7 CFR Part 301). Federal Register, Washington, DC 2007, pp. 8585-8604.
  57. ^ K. Suslow: Recommended Industry Best Management Practices for the Prevention of Phytophthora ramorum Introductions in Nursery Operations . In: Proceedings of the Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2008, pp. 115-128.
  58. ↑ HRI P. ramorum Industry Working Group (Ed.): Nursery Industry Best Management Practices for Phytophthora ramorum to Prevent the Introduction or Establishment in California Nursery Operations 2008.
  59. ↑ SA Tjosvold, DLK Chambers, S. & E. Fichtner: Epidemiology of Phytophthora ramorum Infecting Rhododendrons under Simulated Conditions Nursery . In: Proceedings of the Sudden Oak Death Science Symposium: The State of Our Knowledge . USDA Forest Service, Monterey, CA 2006, pp. 459-461.
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  61. ↑ T. Ufer, M. Posner, H.-P. Wessels, S. Wagner, K. Kaminski, T. Brand, S. Werres: Four Years Experience with Filtration Systems in Commercial Nurseries for Eliminating Phytophthora Species from Recirculation Water . In: Proceedings of the Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2008, p. 111.
  62. ↑ LE Yakabe, JD MacDonald: Soil treatments for the elimination of Phytophthora ramorum from Nursery Beds: Current Knowledge from the Laboratory and the Field . In: Proceedings of the Sudden Oak Death Third Science Symposium . USDA Forest Service, Santa Rosa, CA 2008, pp. 113-114.
  63. ↑ Sudden Oak Death ( English ) suddenoakdeath.org. Retrieved September 21, 2019.
  64. ^ Forestry Commission GB: Phytophthora ramorum - Tree pests and diseases . Retrieved June 25, 2018.
  65. ↑ News: Phytophthora ramorum disease . Archived from the original on April 7, 2012. Retrieved April 18, 2019.

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