Sudden oak death
Encyclopedia
Sudden Oak Death is the common name of a disease caused by the oomycete plant pathogen Phytophthora ramorum. The disease kills oak
and other species of tree and has had devastating effects on the oak populations in California
and Oregon
as well as also being present in Europe
. Symptoms include bleeding canker
s on the tree's trunk
and dieback
of the foliage, in many cases eventually leading to the death of the tree.
P. ramorum also infects a great number of other plant species, significantly rhododendron
s, causing a non-fatal foliage disease known as ramorum dieback. Such plants can act as a source of the inoculum for the disease, with the pathogen producing spore
s that can be transmitted by wind
and rainwater.
P. ramorum was first reported in 1995, and the origins of the pathogen are still unclear but most evidence suggests it was introduced as an exotic species. Very few control mechanisms exist for the disease, and they rely upon early detection and proper disposal of infected plant material.
(in Monterey County
) and southern Humboldt County
. It is confirmed to exist in all coastal counties in this range, as well as in all immediately inland counties from Santa Clara County
north to Lake County
. It has not been found east of the California Coast Ranges, however. It was reported in Curry County, Oregon
(just north of the California border) in 2001. About the same time, a similar disease in continental Europe
and the UK
was also identified as Phytophthora ramorum.
Sonoma County has been hit the hardest, they have more than twice the area of new mortality than any other county in California (http://www.sonoma-county.org/des/pdf/sodsr_plan.pdf)
in 1995 when large numbers of tanoak
s (Lithocarpus densiflorus) died mysteriously, and was described as a new species of Phytophthora
in 2000. It has subsequently been found in many other areas including Britain
, Germany
, and some other U.S.
states, either accidentally introduced in nursery stock, or already present undetected.
In tanoaks, the disease may be recognized by wilting
new shoot
s, older leaves becoming pale green, and after a period of two to three weeks, foliage turns brown while clinging to the branches. Dark brown sap
may stain the lower trunk's bark. Bark may split and exude gum, with visible discoloration. After the tree dies back, suckers will try to sprout the next year, but their tips soon bend and die. Ambrosia beetle
s (Monarthrum scutellare) will most likely infest a dying tree during midsummer, producing piles of fine white dust near tiny holes. Later, bark beetle
s (Pseudopityophthorus pubipennis) produce fine red boring dust. Small black domes, the fruiting bodies of the Hypoxylon
fungus, may also be present on the bark
. Leaf death may occur more than a year after the initial infection and months after the tree has been girdled by beetles.
In Coast Live Oak
s and Californian Black Oaks, the first symptom is a burgundy-red to tar-black thick sap bleeding from the bark surface. These are often referred to as bleeding canker
s.
In addition to oaks, many other forest species may be hosts for the disease, in fact it was observed in the USA that nearly all woody plants in some California
n forest
s were susceptible to P. ramorum. including rhododendron
, Madrone (Arbutus menziesii), Evergreen Huckleberry
(Vaccinium ovatum), California Bay Laurel (Umbellularia californica), Buckeye
(Aesculus californica), Bigleaf Maple
(Acer macrophyllum), Toyon
(Heteromeles arbutifolia), manzanita
(Arctostaphylos spp.), Coast Redwood (Sequoia sempervirens), Douglas-fir
(Pseudotsuga menziesii), Coffeeberry
(Rhamnus californica), Honeysuckle
(Lonicera hispidula) and Shreve's Oak (Quercus parvula v. shrevei). P. ramorum more commonly causes a less severe disease known as Ramorum dieback/leaf blight on these host
s. Characteristic symptoms are dark spots on foliage and in some hosts the dieback of the stems and twigs. The disease is capable of killing some hosts, such as Rhododendron, but most survive. Disease progression on these species is not well documented but hikers have observed dead Douglas-firs with massive quantities of red frass
surrounding their base. Redwoods exhibit needle discoloration and cankers on small branches, with purple lesions on sprouts that may lead to sprout mortality.
In late 2009 the disease was first found in Japanese Larch
trees, in the English
counties of Devon
, Cornwall
and Somerset
.
In August 2010 disease was found in Japanese Larch
trees, in counties Waterford
and Tipperary
in Ireland
.
s (chlamydospores) and zoospore
s, which have flagella enabling swimming
. P. ramorum is spread by air; one of the major mechanisms of dispersal is rainwater splashing spores onto other susceptible plants, and into watercourse
s to be carried for greater distances. Chlamydospore
s can withstand harsh conditions and are able to overwinter. The pathogen will take advantage of wounding, but it is not necessary for infection
to occur.
As mentioned above, P. ramorum does not kill every plant that can be used as a host
, and it is these plants that are most important in the epidemiology
of the disease as they act as sources of inoculum. In the USA bay laurel
seems to be the main source of inoculum in forests. Green waste, such as leaf litter and tree stumps are also capable of supporting P. ramorum as a saprotroph and acting as a source of inoculum. Because P. ramorum is able to infect many ornamental plant
s, it can be transmitted by ornamental plant movement.
Hikers, mountain bike
rs, equestrian
s, and other people engaged in various outdoor activities may also unwittingly move the pathogen into areas where it was not previously present. Those travelling in an area known to be infested with SOD can help prevent the spread of the disease by cleaning their (and their animal's) feet, tires, tools, camping equipment, etc. before returning home or entering another uninfected area, especially if they have been in muddy soil. Additionally, the movement of firewood could serve as a vector for Sudden Oak Death, so both homeowners and travelers alike are advised to buy and burn local firewood.
P. ramorum is heterothallic
and has two mating type
s identified: A1 and A2. Interestingly A1 is found almost exclusively in Europe
and A2 in North America
. Genetics of the two isolates indicate that they are reproductively isolated. On average the A1 mating type is more virulent than the A2 mating type but there is more variation in the pathogenicity of A2 isolates. Because of the genetic and pathological differences it is believed that if the two mating types remain reproductively isolated then two sub-species will be formed.
exists that suggests P. ramorum may be an introduced exotic species, and that these introductions occurred separately for the European and NA populations, hence why only one mating type exists on each continent – this is called a founder effect
. The differences between the two populations are thus caused by adaptation to separate climates. Evidence includes little genetic variability, as Phytophthora ramorum has not had time to diversify since being recently introduced. What variability there is may be explained by multiple introductions with a few individuals adapting best to their respective environments. The behavior of the pathogen in California is also indicative of being introduced; it is assumed that such a high mortality rate of trees would have been noticed sooner if P. ramorum were native
.
Where Phytophthora ramorum did originate remains unclear but most researchers feel Asia
is the most likely, since many of the hosts of P. ramorum originated there. Since certain climates are best suited to P. ramorum, the most likely sources are the Southern Himalayas
, Tibet
or Yunnan province.
have been shown to have evolved by the interspecific hybridization of two different species from the genus
. When a species is introduced into a new environment
it causes episodic selection. The invading species is exposed to other resident taxa
, and hybridization may occur to produce a new species. If these hybrids are successful, they may out compete their parent species. Thus it is possible that Phytophthora ramorum is a hybrid between two species. Its unique morphology
does support this. Also, 3 sequences that were studied to establish the phylogeny of Phytophthora: ITS, cox II and nad 5, were identical supporting Phytophthora ramorum having recently evolved.
structure. Alternatively, the symptoms of Phytophthora ramorum may have been mistaken for that of other pathogens. When SOD first appeared in the USA, many other pathogens and conditions were blamed before P. ramorum was found to be the causal agent. With many of the most seriously affected plants being in the forest, the likelihood of seeing diseased trees is also low.
Additional long-term impacts of SOD may also be inferred from regeneration patterns in areas that have experienced severe mortality. Current regeneration patterns may indicate which tree species will replace tanoak in diseased areas; such transitions will be of particular importance in forest types that were relatively poor in tree species diversity even before the introduction of SOD (e.g. redwood forest). The only scientific study to comprehensively examine regeneration in SOD-impacted redwood forests found no evidence that other broadleaf tree species are beginning to recruit; the researchers instead observed that redwood was colonizing most mortality gaps. However, they also found inadequate regeneration in some areas and concluded that definitive regeneration patterns have not yet manifested. In addition, this study only considered one study site (in Marin County, CA) and thus additional studies are needed before broad generalizations can be stated.
Detecting the presence of Phytophthora species requires laboratory confirmation. The traditional method of culturing is on a growth medium that is selective against fungi (and, in some cases, against other oomycetes such as Pythium
species). Host material is removed from the leading edge of a plant tissue canker caused by the pathogen; resulting growth is examined under a microscope
to confirm the unique morphology
of P. ramorum. Successful isolation of the pathogen often depends on the type of host tissue and the time of year that detection is attempted.
Because of these difficulties, researchers have developed some other approaches for identifying P. ramorum. The ELISA
(enzyme-linked immunosorbent assay) test can be the first step in non-culture methods of identifying P. ramorum, but it can only be a first step, because it detects the presence of proteins that are produced by all Phytophthora species. In other words, it can identify to the Phytophthora genus
level, but not to the species
level. ELISA tests can process large numbers of samples at once, so researchers often use it to screen out samples that are likely positive from those that are not when the total number of samples is very large. Some manufacturers produce small-scale ELISA “field kits” that the homeowner can use to determine if plant tissue is infected by Phytophthora.
Researchers have also developed numerous molecular techniques for P. ramorum identification. These include amplifying DNA
sequences in the internal transcribed spacer
region of the P. ramorum genome
(ITS Polymerase Chain Reaction
, or ITS PCR); real-time PCR, in which DNA abundance is measured in real time during the PCR reaction, using dyes or probes such as SBYR-Green or TaqMan; multiplex PCR, which amplifies more than one region of DNA at the same time; and Single Strand Conformation Polymorphism
(SSCP), which uses the ITS DNA sequence amplified by the PCR reaction to differentiate Phytophthora species according to their differential movement through a gel.
Additionally, researchers have begun using features of the DNA sequence of P. ramorum to pinpoint the minuscule differences of separate P. ramorum isolates from each other. Two techniques for doing this are amplified fragment length polymorphism
, which through comparing differences between various fragments in the sequence has enabled researchers to differentiate correctly between EU and U.S. isolates, and the examination of microsatellites, which are areas on the sequence featuring repeating base pairs. When P. ramorum propagules arrive in a new geographic location and establish colonies, these microsatellites begin to display mutation
in a relatively short time, and they mutate in a stepwise fashion. Based on this, researchers in California have been able to construct trees, based on microsatellite analyses of isolates collected from around the state, that trace the movement of P. ramorum from two likely initial points of establishment in Marin
and Santa Cruz
counties and out to subsequent points.
Early detection of P. ramorum on a landscape scale begins with the observation of symptoms on individual plants (and/or detecting P. ramorum propagules in watercourses; see below). Systematic ground-based monitoring has been difficult within the range of P. ramorum because most infected trees stand on a complex mosaic of lands with various ownerships. In some areas, targeted ground-based surveys have been conducted in areas of heavy recreation or visitor use such as parks, trailheads, and boat ramps. In California, when conducting ground-based detection, looking for symptoms on bay laurel is the most effective strategy, since P. ramorum infection of true oaks and tanoaks is almost always highly associated with bay laurel, the main epidemiological springboard for the pathogen. Moreover, on many sites in California (though not all), P. ramorum can typically be detected from infected bay laurel tissues via culturing techniques year-round; this is not the case for most other hosts, nor is it the case in Oregon, where tanoak is the most reliable host.
As part of a nationwide USDA program, a ground-based detection survey was implemented from 2003 to 2006 in thirty-nine U.S. states to determine whether the pathogen was established outside the West Coast areas already known to be infested. Sampling areas were stratified by environmental variables likely to be conducive to pathogen growth and by proximity to possible points of inoculum introduction such as nurseries. Samples were collected along transects established in potentially susceptible forests or outside the perimeters of nurseries. The only positive samples were collected in California, confirming that P. ramorum was not yet established in the environment outside the West Coast.
Aerial surveying has proven useful for detection of P. ramorum infestations across large landscapes, although it is not as “early” a technique as some others because it depends on spotting dead tanoak crowns from fixed-wing aircraft. Sophisticated GPS and sketch-mapping technology enables spotters to mark the locations of dead trees so that ground crews can return to the area to sample from nearby vegetation.
Detection of P. ramorum in watercourses has emerged as the earliest of early detection methods. This technique employs pear
or rhododendron
baits suspended in the watercourse using ropes, buckets, mesh bags, or other similar devices. If plants in the watershed are infected with P. ramorum, zoospores of the pathogen (as well as other Phytophthora spp.) are likely present in adjacent waterways. Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay. This method has detected P. ramorum at scales ranging from small, intermittent seasonal drainages to the Garcia, Chetco, and South Fork Eel Rivers in California and Oregon (144, 352, and 689 mi2 drainage areas, respectively). It can detect the existence of infected plants in watersheds before any mortality from the infections becomes evident. Of course, it cannot detect the exact locations of those infected plants: at the first sign of P. ramorum propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.
A less technical means of detecting P. ramorum at the landscape level involves engaging local landowners across the landscape in the search. Many local county Agriculture Departments and University of California Cooperative Extension offices in California have been able to keep track of the distribution of the pathogen in their regions through reports and samples brought to them by the public. In 2008, the Garbelotto Laboratory at UC Berkeley, along with local collaborators, hosted a series of educational events, called “SOD Blitzes,” designed to give local landowners basic information about P. ramorum and how to identify its symptoms; each participant was provided with a sampling kit, sampled a certain number of trees on his or her property, and returned the samples to the lab for analysis. It is hoped that this kind of “citizen science” can help generate an improved map of P. ramorum distribution in the areas where the workshops are held.
ownership). The eradication campaign involves vigorous early detection by airplane and watercourse monitoring, a U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) and Oregon Department of Agriculture-led quarantine
to prevent movement of host materials out of the area where infected trees are found, and immediate removal of P. ramorum host vegetation, symptomatic or not, within a 300 feet (91.4 m) buffer around each infected tree.
The Oregon eradication effort, which began near the town of Brookings
in southwest Oregon in 2001, has adapted its management efforts over the years in response to new information about P. ramorum. For example, after inoculation trials of various tree species more clearly delineated which hosts are susceptible, the Oregon cooperators began leaving non-host species such as Douglas-fir and red alder on site. In another example, after finding that a small percentage of tanoak stumps that were resprouting on the host removal sites were infected with the pathogen—whether these infections were systemic or reached the sprouts from the surrounding environment is unknown—the cooperators began pretreating trees with very small, targeted amounts of herbicide
to kill the root systems of infected tanoaks before cutting them down. The effort has been successful in that while it has not yet completely eradicated the pathogen from Oregon forests, the epidemic in Oregon has not taken the explosive course that it has in California forests.
California, on the other hand, faces significant obstacles that preclude it from mounting the same kind of eradication effort. For one thing, the organism was too well established in forests in the Santa Cruz
and San Francisco Bay
areas by the time the cause of Sudden Oak Death was discovered to enable any eradication effort to succeed. Even in still relatively uninfested areas of the north coast and southern Big Sur
, regionally coordinated efforts to manage the pathogen face huge challenges of leadership, coordination, and funding. Nevertheless, land managers are still working to coordinate efforts between states, counties, and agencies to provide P. ramorum management in a more comprehensive manner.
Several options exist for landowners who want to treat to limit the impacts of Sudden Oak Death on their properties. None of these options is foolproof, guaranteed to eradicate P. ramorum, or guaranteed to prevent a tree from becoming infected. Some are still in the initial stage of testing. Nevertheless, when used thoughtfully and thoroughly, some of the treatments do improve the likelihood of either slowing the spread of the pathogen or of limiting its impacts on trees or stands of trees. Assuming that the landowner has correctly identified the host tree(s) and symptom(s), has submitted a sample to a local authority to send to an approved laboratory for testing, and has received confirmation that the tree(s) are indeed infected with P. ramorum—or, alternatively, assuming that the landowner knows that P. ramorum-infected trees are nearby and wants to protect the resources on his or her property—he or she can attempt control by cultural (individual-tree), chemical, or silvicultural (stand-level) means.
The best evidence that cultural techniques might help protect trees against P. ramorum comes from research that has established a correlation between disease risk in coast live oak trees and the trees’ proximity to bay laurel. In particular, this research found that bay laurel trees growing within 5m of the trunk of an oak tree were the best predictors of disease risk. This implies that strategic removal of bay laurel trees near coast live oaks might decrease the risk of oak infection. Wholesale removal of bay laurel trees would not be warranted, since the bay laurels close to the oak trees appear to provide the greatest risk factor. Whether the same pattern is true for other oaks or tanoaks has yet to be established. Research on this subject has been started for tanoak, but any eventual cultural recommendations will be more complicated, because tanoak twigs also serve as sources of P. ramorum inoculum.
A promising treatment for preventing infection of individual oak and tanoak trees—not for curing an already established infection—is a phosphonate
fungicide
marketed under the trade name Agri-fos. Phosphonate is a neutralized form of phosphorous acid that works not by direct antagonism of Phytophthora, but by stimulating various of kinds of immune responses on the part of the tree. It is mostly environmentally benign if not applied to non-target plants and can be applied either as an injection into the tree stem or as a spray to the bole. When applying Agri-fos as a spray, it must be combined with an organosilicate surfactant
, Pentra-bark, to enable the product to adhere to the bole long enough to be absorbed by the tree. Agri-fos has been very effective in preventing tree infections, but it must be applied when visible symptoms of P. ramorum on other trees in the immediate neighborhood are still relatively distant; otherwise, it is likely that the tree one wishes to treat is already infected but that visible symptoms have not yet developed (this is especially true for tanoak).
Trials of silvicultural methods for treating P. ramorum began in Humboldt County
in northwest coastal California in 2006. The trials have taken place on a variety of infested properties both private and public and have generally focused on varying levels and kinds of host removal. The largest (50 acres (202,343 m²)) and most replicated trials have involved removal of tanoak and bay laurel by chainsaw
throughout the infested stand, both with and without subsequent underburning designed to eliminate small seedlings and infested leaf litter. Other treatments included host removal in a modified “shaded fuelbreak” design in which all bay laurel is removed, but not all tanoaks; bay and tanoak removal using herbicides; and removal of bay laurel alone. The results of these treatments are still being monitored, but repeated sampling has so far detected only very small amounts of P. ramorum in the soil or on vegetation in the treated sites.
An array of studies have tested the curative and protective effects of various chemical compounds against P. ramorum in plants valued as ornamentals or Christmas trees. Many studies have focused on the four main ornamental hosts of P. ramorum (Rhododendron
, Camellia
, Viburnum
, and Pieris
). Several effective compounds have been found; some of the most effective include mefenoxam, metalaxyl
, dimethomorph, and fenamidone
. Many of these studies have converged upon the following conclusions: chemical compounds are, in general, more effective as preventatives than in curatives; when used preventatively, chemical compounds must be reapplied at various intervals; and chemical compounds can mask the symptoms of P. ramorum infection in the host plant, potentially interfering with inspections for quarantine efforts. In general, these compounds suppress but do not eradicate the pathogen, and some researchers are concerned that with repeated use the pathogen may become resistant to them. These studies and conclusions are summarized by Kliejunas.
Another area of research and evolving practice deals with eliminating P. ramorum from nursery environments in which it is established to prevent human-mediated pathogen movement within the ornamental plant trade. One way of approaching this is through a robust quarantine and inspection program, which the various federal and state regulatory agencies have implemented. Under the federal P. ramorum quarantine program implemented by USDA APHIS
, nurseries in California, Oregon, and Washington are regulated and must participate in an annual inspection regime; nurseries in the fourteen infested counties in coastal California, plus the limited infested area in Curry County
, Oregon, must participate in a more stringent inspection schedule when shipping out of this area.
Much of the research into disinfesting nurseries has focused on the voluntary Best Management Practices (BMPs) that nurseries can implement to prevent P. ramorum’s introduction into the nursery and movement from plant to plant. In 2008, a group of nursery industry organizations issued a list of BMPs that includes subsections on Pest Prevention/Management, Training, Internal/External Monitoring/Audits, Records/Traceability, and Documentation. The document includes such specific recommendations as “Avoid overhead irrigation
of high-risk plants”; “After every crop rotation
, disinfect propagation
mist beds, sorting area, cutting benches, machines and tools to minimize the spread or introduction of pathogens”; and “Nursery personnel should attend one or more P. ramorum trainings conducted by qualified personnel or document self-training”.
Research on control of P. ramorum in nurseries has also focused on disinfesting irrigation water containing P. ramorum inoculum. Irrigation water can become infested from bay trees in the forest (if the irrigation source is a stream), from bay trees overhanging irrigation ponds, from runoff from infested forests, or from recirculated irrigation water. Experiments in Germany with three types of filters—slow sand filters, lava filter
s, and constructed wetlands—showed that the first two removed P. ramorum from the irrigation water completely, while 37% of the post-treatment water samples from the constructed wetland still contained P. ramorum.
Since P. ramorum can persist for an undetermined period of time within the soil profile, management programs in nurseries should also deal with delineating the pathogen’s distribution in nursery soil and eliminating it from infested areas. A variety of chemical options have been tested for soil disinfestation, including such chemicals as chloropicrin
, metham sodium
, iodomethane
and dazomet. Lab tests indicated that all of these chemicals were effective when applied to infested soil in glass jars. Additionally, tests on volunteer nurseries with infested soil demonstrated that dazomet (trade name Basamid) fumigation followed by a 14-day tarping period successfully removed P. ramorum from the soil profile. Other soil disinfestation practices under investigation, or in which interest has been expressed, include steam sterilization
, solarization
, and paving of infested areas.
and USDA Forest Service have implemented guidelines and mitigation requirements for the latter two situations; basic information about cleanliness in P. ramorum-infested areas can be found at the California Oak Mortality Task Force web site (www.suddenoakdeath.org) under the “Treatment and Management” section (subsection “Sanitation and Reducing Spread”).
in 2009, the Forestry Commission
, DEFRA, the Food and Environment Research Agency
, Cornwall County Council
, and Natural England
are working together to record the locations and deal with this disease. Natural England
is offering grant funding through its Environmental Stewardship
, Countryside Stewardship and Environmentally Sensitive Area
schemes to clear rhododendron. In 2011, the Forestry Commission
started felling 10000 acres (40.5 km²) of larch
forest in the SW of England, as an attempt to halt the spread of the disease.
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
and other species of tree and has had devastating effects on the oak populations in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
as well as also being present in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. Symptoms include bleeding canker
Canker
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately...
s on the tree's trunk
Trunk (botany)
In botany, trunk refers to the main wooden axis of a tree that supports the branches and is supported by and directly attached to the roots. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the...
and dieback
Dieback
Dieback may refer to a number of plant problems and diseases including:* Forest dieback caused by acid rain, heavy metal pollution, or imported pathogens* The death of regions of a plant or similar organism caused by physical damage, such as from pruning...
of the foliage, in many cases eventually leading to the death of the tree.
P. ramorum also infects a great number of other plant species, significantly rhododendron
Rhododendron
Rhododendron is a genus of over 1 000 species of woody plants in the heath family, most with showy flowers...
s, causing a non-fatal foliage disease known as ramorum dieback. Such plants can act as a source of the inoculum for the disease, with the pathogen producing spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s that can be transmitted by wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
and rainwater.
P. ramorum was first reported in 1995, and the origins of the pathogen are still unclear but most evidence suggests it was introduced as an exotic species. Very few control mechanisms exist for the disease, and they rely upon early detection and proper disposal of infected plant material.
Presence
The disease is known to exist in California's coastal region between Big SurBig Sur
Big Sur is a sparsely populated region of the Central Coast of California where the Santa Lucia Mountains rise abruptly from the Pacific Ocean. The name "Big Sur" is derived from the original Spanish-language "el sur grande", meaning "the big south", or from "el país grande del sur", "the big...
(in Monterey County
Monterey County, California
Monterey County is a county located on the Pacific coast of the U.S. state of California, its northwestern section forming the southern half of Monterey Bay. The northern half of the bay is in Santa Cruz County. As of 2010, the population was 415,057. The county seat and largest city is Salinas...
) and southern Humboldt County
Humboldt County, California
Humboldt County is a county in the U.S. state of California, located on the far North Coast 200 miles north of San Francisco. According to 2010 Census Data, the county’s population was 134,623...
. It is confirmed to exist in all coastal counties in this range, as well as in all immediately inland counties from Santa Clara County
Santa Clara County, California
Santa Clara County is a county located at the southern end of the San Francisco Bay Area in the U.S. state of California. As of 2010 it had a population of 1,781,642. The county seat is San Jose. The highly urbanized Santa Clara Valley within Santa Clara County is also known as Silicon Valley...
north to Lake County
Lake County, California
Lake County is a county located in the north central portion of the U.S. state of California, north of the San Francisco Bay Area. It takes its name from Clear Lake, the dominant geographic feature in the county and the largest natural lake wholly within California...
. It has not been found east of the California Coast Ranges, however. It was reported in Curry County, Oregon
Curry County, Oregon
Curry County is a county located in the U.S. state of Oregon. In 2010, its population was 22,364. The county is named for George Law Curry, a governor of the Oregon Territory. The seat of the county is Gold Beach.-Economy:...
(just north of the California border) in 2001. About the same time, a similar disease in continental Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
was also identified as Phytophthora ramorum.
Sonoma County has been hit the hardest, they have more than twice the area of new mortality than any other county in California (http://www.sonoma-county.org/des/pdf/sodsr_plan.pdf)
Hosts and symptoms
It was first discovered in CaliforniaCalifornia
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
in 1995 when large numbers of tanoak
Tanoak
Tanoak, formerly known taxonomically as Lithocarpus densiflorus, was recently moved into a new genus, Notholithocarpus, based on multiple lines of evidence....
s (Lithocarpus densiflorus) died mysteriously, and was described as a new species of Phytophthora
Phytophthora
Phytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The genus was first described by Heinrich Anton de Bary in 1875...
in 2000. It has subsequently been found in many other areas including Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and some other U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
states, either accidentally introduced in nursery stock, or already present undetected.
In tanoaks, the disease may be recognized by wilting
Wilting
Wilting refers to the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells...
new shoot
Shoot
Shoots are new plant growth, they can include stems, flowering stems with flower buds, and leaves. The new growth from seed germination that grows upward is a shoot where leaves will develop...
s, older leaves becoming pale green, and after a period of two to three weeks, foliage turns brown while clinging to the branches. Dark brown sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...
may stain the lower trunk's bark. Bark may split and exude gum, with visible discoloration. After the tree dies back, suckers will try to sprout the next year, but their tips soon bend and die. Ambrosia beetle
Ambrosia beetle
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae , which live in nutritional symbiosis with ambrosia fungi and probably with bacteria...
s (Monarthrum scutellare) will most likely infest a dying tree during midsummer, producing piles of fine white dust near tiny holes. Later, bark beetle
Bark beetle
A bark beetle is one of approximately 220 genera with 6,000 species of beetles in the subfamily Scolytinae. Traditionally, this was considered a distinct family Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true weevil" family...
s (Pseudopityophthorus pubipennis) produce fine red boring dust. Small black domes, the fruiting bodies of the Hypoxylon
Hypoxylon
Hypoxylon is a genus of Ascomycetes commonly found on dead wood, and usually one of the earliest species to colonise dead wood. A common European species is Hypoxylon fragiforme which is particular common on dead trunks of beech.-External links:*...
fungus, may also be present on the bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
. Leaf death may occur more than a year after the initial infection and months after the tree has been girdled by beetles.
In Coast Live Oak
Coast Live Oak
Quercus agrifolia, the Coast Live Oak, is an evergreen oak , native to the California Floristic Province. It grows west of the Sierra Nevada from Mendocino County, California, south to northern Baja California in Mexico. It is classified in the red oak section Quercus agrifolia, the Coast Live Oak,...
s and Californian Black Oaks, the first symptom is a burgundy-red to tar-black thick sap bleeding from the bark surface. These are often referred to as bleeding canker
Canker
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately...
s.
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
n forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
s were susceptible to P. ramorum. including rhododendron
Rhododendron
Rhododendron is a genus of over 1 000 species of woody plants in the heath family, most with showy flowers...
, Madrone (Arbutus menziesii), Evergreen Huckleberry
Huckleberry
Huckleberry is a common name used in North America for several species of plants in two closely related genera in the family Ericaceae:* Vaccinium* GaylussaciaHuckleberry may also refer to:-Plants:...
(Vaccinium ovatum), California Bay Laurel (Umbellularia californica), Buckeye
Aesculus californica
Aesculus californica is a species of buckeye that is native [ |] to California and southwest Oregon [Jackson, County], and the only buckeye native to these states.-Description:...
(Aesculus californica), Bigleaf Maple
Bigleaf Maple
Acer macrophyllum is a large deciduous tree in the genus Acer.It can grow to be up to 35 m tall, but more commonly grows 15 m to 20 m tall. It is native to western North America, mostly near the Pacific coast, from southernmost Alaska to southern California...
(Acer macrophyllum), Toyon
Toyon
Heteromeles arbutifolia , and commonly known as Toyon, is a common perennial shrub native to California down to Baja California....
(Heteromeles arbutifolia), manzanita
Manzanita
Manzanita is a common name for many species of the genus Arctostaphylos. They are evergreen shrubs or small trees present in the chaparral biome of western North America, where they occur from southern British Columbia, Washington to California, Arizona and New Mexico in the United States, and...
(Arctostaphylos spp.), Coast Redwood (Sequoia sempervirens), Douglas-fir
Douglas-fir
Douglas-fir is one of the English common names for evergreen coniferous trees of the genus Pseudotsuga in the family Pinaceae. Other common names include Douglas tree, and Oregon pine. There are five species, two in western North America, one in Mexico, and two in eastern Asia...
(Pseudotsuga menziesii), Coffeeberry
Rhamnus californica
Rhamnus californica , is called coffeeberry because its berries contain seeds which look like coffee beans—it is also called California buckthorn...
(Rhamnus californica), Honeysuckle
Honeysuckle
Honeysuckles are arching shrubs or twining vines in the family Caprifoliaceae, native to the Northern Hemisphere. There are about 180 species of honeysuckle, 100 of which occur in China; Europe, India and North America have only about 20 native species each...
(Lonicera hispidula) and Shreve's Oak (Quercus parvula v. shrevei). P. ramorum more commonly causes a less severe disease known as Ramorum dieback/leaf blight on these host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
s. Characteristic symptoms are dark spots on foliage and in some hosts the dieback of the stems and twigs. The disease is capable of killing some hosts, such as Rhododendron, but most survive. Disease progression on these species is not well documented but hikers have observed dead Douglas-firs with massive quantities of red frass
Frass
Frass is the fine powdery material phytophagous insects pass as waste after digesting plant parts. It causes plants to excrete chitinase due to high chitin levels, it is a natural bloom stimulant, and has high nutrient levels. Frass is known to have abundant amoeba, beneficial bacteria, and fungi...
surrounding their base. Redwoods exhibit needle discoloration and cankers on small branches, with purple lesions on sprouts that may lead to sprout mortality.
In late 2009 the disease was first found in Japanese Larch
Japanese Larch
Japanese Larch is a species of larch native to Japan, in the mountains of Chūbu and Kantō regions in central Honshū....
trees, in the English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
counties of Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
, Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
and Somerset
Somerset
The ceremonial and non-metropolitan county of Somerset in South West England borders Bristol and Gloucestershire to the north, Wiltshire to the east, Dorset to the south-east, and Devon to the south-west. It is partly bounded to the north and west by the Bristol Channel and the estuary of the...
.
In August 2010 disease was found in Japanese Larch
Japanese Larch
Japanese Larch is a species of larch native to Japan, in the mountains of Chūbu and Kantō regions in central Honshū....
trees, in counties Waterford
Waterford
Waterford is a city in the South-East Region of Ireland. It is the oldest city in the country and fifth largest by population. Waterford City Council is the local government authority for the city and its immediate hinterland...
and Tipperary
Tipperary
Tipperary is a town and a civil parish in South Tipperary in Ireland. Its population was 4,415 at the 2006 census. It is also an ecclesiastical parish in the Roman Catholic Archdiocese of Cashel and Emly, and is in the historical barony of Clanwilliam....
in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
.
Transmission
P. ramorum produces both resting sporeSpore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s (chlamydospores) and zoospore
Zoospore
A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some algae, bacteria and fungi to propagate themselves.-Flagella:...
s, which have flagella enabling swimming
Aquatic locomotion
Swimming is biologically propelled motion through a liquid medium. Swimming has evolved a number of times in a range of organisms ranging from arthropods to fish to molluscs.-Evolution of swimming:...
. P. ramorum is spread by air; one of the major mechanisms of dispersal is rainwater splashing spores onto other susceptible plants, and into watercourse
Watercourse
A watercourse is any flowing body of water. These include rivers, streams, anabranches, and so forth.-See also:* physical geography* Environmental flow* Waterway* Hydrology* Wadi-External links:...
s to be carried for greater distances. Chlamydospore
Chlamydospore
A Chlamydospore is the thick-walled big resting spore of several kinds of fungi. It is the life-stage which survives in unfavourable conditions, such as dry or hot seasons....
s can withstand harsh conditions and are able to overwinter. The pathogen will take advantage of wounding, but it is not necessary for infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
to occur.
As mentioned above, P. ramorum does not kill every plant that can be used as a host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
, and it is these plants that are most important in the epidemiology
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
of the disease as they act as sources of inoculum. In the USA bay laurel
Bay Laurel
The bay laurel , also known as sweet bay, bay tree, true laurel, Grecian laurel, laurel tree, or simply laurel, is an aromatic evergreen tree or large shrub with green, glossy leaves, native to the Mediterranean region. It is the source of the bay leaf used in cooking...
seems to be the main source of inoculum in forests. Green waste, such as leaf litter and tree stumps are also capable of supporting P. ramorum as a saprotroph and acting as a source of inoculum. Because P. ramorum is able to infect many ornamental plant
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
s, it can be transmitted by ornamental plant movement.
Hikers, mountain bike
Mountain bike
A mountain bike or mountain bicycle is a bicycle created for off-road cycling. This activity includes traversing of rocks and washouts, and steep declines,...
rs, equestrian
Equestrianism
Equestrianism more often known as riding, horseback riding or horse riding refers to the skill of riding, driving, or vaulting with horses...
s, and other people engaged in various outdoor activities may also unwittingly move the pathogen into areas where it was not previously present. Those travelling in an area known to be infested with SOD can help prevent the spread of the disease by cleaning their (and their animal's) feet, tires, tools, camping equipment, etc. before returning home or entering another uninfected area, especially if they have been in muddy soil. Additionally, the movement of firewood could serve as a vector for Sudden Oak Death, so both homeowners and travelers alike are advised to buy and burn local firewood.
The two mating types
Heterothallic
Heterothallic species have sexes that reside in different individuals....
and has two mating type
Mating type
Mating types occur in eukaryotes that undergo sexual reproduction via isogamy. Since the gametes of different mating types look alike, they are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female." Mating can only take place between different mating...
s identified: A1 and A2. Interestingly A1 is found almost exclusively in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and A2 in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Genetics of the two isolates indicate that they are reproductively isolated. On average the A1 mating type is more virulent than the A2 mating type but there is more variation in the pathogenicity of A2 isolates. Because of the genetic and pathological differences it is believed that if the two mating types remain reproductively isolated then two sub-species will be formed.
Possible origins
P. ramorum is a relatively new disease, and there have been several debates about where it may have originated or how it evolved.Introduction as an exotic species
EvidenceEvidence
Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...
exists that suggests P. ramorum may be an introduced exotic species, and that these introductions occurred separately for the European and NA populations, hence why only one mating type exists on each continent – this is called a founder effect
Founder effect
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall...
. The differences between the two populations are thus caused by adaptation to separate climates. Evidence includes little genetic variability, as Phytophthora ramorum has not had time to diversify since being recently introduced. What variability there is may be explained by multiple introductions with a few individuals adapting best to their respective environments. The behavior of the pathogen in California is also indicative of being introduced; it is assumed that such a high mortality rate of trees would have been noticed sooner if P. ramorum were native
Indigenous (ecology)
In biogeography, a species is defined as native to a given region or ecosystem if its presence in that region is the result of only natural processes, with no human intervention. Every natural organism has its own natural range of distribution in which it is regarded as native...
.
Where Phytophthora ramorum did originate remains unclear but most researchers feel Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
is the most likely, since many of the hosts of P. ramorum originated there. Since certain climates are best suited to P. ramorum, the most likely sources are the Southern Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
, Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...
or Yunnan province.
Hybridization events
Species of PhytophthoraPhytophthora
Phytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The genus was first described by Heinrich Anton de Bary in 1875...
have been shown to have evolved by the interspecific hybridization of two different species from the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. When a species is introduced into a new environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
it causes episodic selection. The invading species is exposed to other resident taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, and hybridization may occur to produce a new species. If these hybrids are successful, they may out compete their parent species. Thus it is possible that Phytophthora ramorum is a hybrid between two species. Its unique morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
does support this. Also, 3 sequences that were studied to establish the phylogeny of Phytophthora: ITS, cox II and nad 5, were identical supporting Phytophthora ramorum having recently evolved.
A native organism
It is possible that Phytophthora ramorum is native to the USA. Infection rates could have previously been at a low level, but changes in the environment caused a change to the populationPopulation
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
structure. Alternatively, the symptoms of Phytophthora ramorum may have been mistaken for that of other pathogens. When SOD first appeared in the USA, many other pathogens and conditions were blamed before P. ramorum was found to be the causal agent. With many of the most seriously affected plants being in the forest, the likelihood of seeing diseased trees is also low.
Ecological impacts
In addition to the direct impacts of this emerging disease (tree mortality), numerous indirect effects will inevitably manifest. Many of the most serious changes will not be apparent for decades, but several predictions of long-term impacts have been proposed in the scientific literature (e.g.). While such predictions are necessarily speculative, indirect impacts occurring on shorter time scales have been documented in a few cases. For instance, one study demonstrated that redwood trees increased their growth rates after neighboring tanoaks were killed by sudden oak death. Other studies have combined current observations and reconstruction/projection techniques to document short-term impacts while also inferring future conditions; as an example, one recent open-access publication used this approach to investigate the effects of sudden oak death on structural characteristics of redwood forests.Additional long-term impacts of SOD may also be inferred from regeneration patterns in areas that have experienced severe mortality. Current regeneration patterns may indicate which tree species will replace tanoak in diseased areas; such transitions will be of particular importance in forest types that were relatively poor in tree species diversity even before the introduction of SOD (e.g. redwood forest). The only scientific study to comprehensively examine regeneration in SOD-impacted redwood forests found no evidence that other broadleaf tree species are beginning to recruit; the researchers instead observed that redwood was colonizing most mortality gaps. However, they also found inadequate regeneration in some areas and concluded that definitive regeneration patterns have not yet manifested. In addition, this study only considered one study site (in Marin County, CA) and thus additional studies are needed before broad generalizations can be stated.
Early detection
Early detection of P. ramorum is essential for its control. On an individual-tree basis, preventative treatments, which are more effective than therapeutic treatments, depend on knowledge of the pathogen’s movement through the landscape to know when it is nearing prized trees. On the landscape level, P. ramorum’s fast and often undetectable movement means that any treatment hoping to slow its spread must happen very early in the development of an infestation. Since P. ramorum’s discovery, researchers have been working on the development of early detection methods on scales ranging from diagnosis in individual infected plants to landscape-level detection efforts involving large numbers of people.Detecting the presence of Phytophthora species requires laboratory confirmation. The traditional method of culturing is on a growth medium that is selective against fungi (and, in some cases, against other oomycetes such as Pythium
Pythium
Pythium is a genus of parasitic oomycete. Most species are plant parasites, but Pythium insidiosum is an important pathogen of animals...
species). Host material is removed from the leading edge of a plant tissue canker caused by the pathogen; resulting growth is examined under a microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
to confirm the unique morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
of P. ramorum. Successful isolation of the pathogen often depends on the type of host tissue and the time of year that detection is attempted.
Because of these difficulties, researchers have developed some other approaches for identifying P. ramorum. The ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
(enzyme-linked immunosorbent assay) test can be the first step in non-culture methods of identifying P. ramorum, but it can only be a first step, because it detects the presence of proteins that are produced by all Phytophthora species. In other words, it can identify to the Phytophthora genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
level, but not to the species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
level. ELISA tests can process large numbers of samples at once, so researchers often use it to screen out samples that are likely positive from those that are not when the total number of samples is very large. Some manufacturers produce small-scale ELISA “field kits” that the homeowner can use to determine if plant tissue is infected by Phytophthora.
Researchers have also developed numerous molecular techniques for P. ramorum identification. These include amplifying DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
sequences in the internal transcribed spacer
Internal transcribed spacer
ITS refers to a piece of non-functional RNA situated between structural ribosomal RNAs on a common precursor transcript. Read from 5' to 3', this polycistronic rRNA precursor transcript contains the 5' external transcribed sequence , 18S rRNA, ITS1, 5.8S rRNA, ITS2, 28S rRNA and finally the 3'ETS...
region of the P. ramorum genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
(ITS Polymerase Chain Reaction
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
, or ITS PCR); real-time PCR, in which DNA abundance is measured in real time during the PCR reaction, using dyes or probes such as SBYR-Green or TaqMan; multiplex PCR, which amplifies more than one region of DNA at the same time; and Single Strand Conformation Polymorphism
Single strand conformation polymorphism
Single-strand conformation polymorphism , or single-strand chain polymorphism, is defined as conformational difference of single-stranded nucleotide sequences of identical length as induced by differences in the sequences under certain experimental conditions...
(SSCP), which uses the ITS DNA sequence amplified by the PCR reaction to differentiate Phytophthora species according to their differential movement through a gel.
Additionally, researchers have begun using features of the DNA sequence of P. ramorum to pinpoint the minuscule differences of separate P. ramorum isolates from each other. Two techniques for doing this are amplified fragment length polymorphism
Amplified fragment length polymorphism
Amplified Fragment Length Polymorphism PCR is a PCR-based tool used in genetics research, DNA fingerprinting, and in the practice of genetic engineering. Developed in the early 1990s by Keygene, AFLP uses restriction enzymes to digest genomic DNA, followed by ligation of adaptors to the sticky...
, which through comparing differences between various fragments in the sequence has enabled researchers to differentiate correctly between EU and U.S. isolates, and the examination of microsatellites, which are areas on the sequence featuring repeating base pairs. When P. ramorum propagules arrive in a new geographic location and establish colonies, these microsatellites begin to display mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
in a relatively short time, and they mutate in a stepwise fashion. Based on this, researchers in California have been able to construct trees, based on microsatellite analyses of isolates collected from around the state, that trace the movement of P. ramorum from two likely initial points of establishment in Marin
Marin
-Places:*Marin, Haute-Savoie, a commune in France*Le Marin, a commune in the French overseas department of Martinique*Marín, Nuevo León, a town and municipality in Mexico*Marín, Pontevedra, a municipality in Galicia, Spain*Marin County, California...
and Santa Cruz
Santa Cruz County, California
Santa Cruz County is a county located on the Pacific coast of the U.S. state of California, on the California Central Coast. The county forms the northern coast of the Monterey Bay. . As of the 2010 U.S. Census, its population was 262,382. The county seat is Santa Cruz...
counties and out to subsequent points.
Early detection of P. ramorum on a landscape scale begins with the observation of symptoms on individual plants (and/or detecting P. ramorum propagules in watercourses; see below). Systematic ground-based monitoring has been difficult within the range of P. ramorum because most infected trees stand on a complex mosaic of lands with various ownerships. In some areas, targeted ground-based surveys have been conducted in areas of heavy recreation or visitor use such as parks, trailheads, and boat ramps. In California, when conducting ground-based detection, looking for symptoms on bay laurel is the most effective strategy, since P. ramorum infection of true oaks and tanoaks is almost always highly associated with bay laurel, the main epidemiological springboard for the pathogen. Moreover, on many sites in California (though not all), P. ramorum can typically be detected from infected bay laurel tissues via culturing techniques year-round; this is not the case for most other hosts, nor is it the case in Oregon, where tanoak is the most reliable host.
As part of a nationwide USDA program, a ground-based detection survey was implemented from 2003 to 2006 in thirty-nine U.S. states to determine whether the pathogen was established outside the West Coast areas already known to be infested. Sampling areas were stratified by environmental variables likely to be conducive to pathogen growth and by proximity to possible points of inoculum introduction such as nurseries. Samples were collected along transects established in potentially susceptible forests or outside the perimeters of nurseries. The only positive samples were collected in California, confirming that P. ramorum was not yet established in the environment outside the West Coast.
Aerial surveying has proven useful for detection of P. ramorum infestations across large landscapes, although it is not as “early” a technique as some others because it depends on spotting dead tanoak crowns from fixed-wing aircraft. Sophisticated GPS and sketch-mapping technology enables spotters to mark the locations of dead trees so that ground crews can return to the area to sample from nearby vegetation.
Detection of P. ramorum in watercourses has emerged as the earliest of early detection methods. This technique employs pear
Pear
The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
or rhododendron
Rhododendron
Rhododendron is a genus of over 1 000 species of woody plants in the heath family, most with showy flowers...
baits suspended in the watercourse using ropes, buckets, mesh bags, or other similar devices. If plants in the watershed are infected with P. ramorum, zoospores of the pathogen (as well as other Phytophthora spp.) are likely present in adjacent waterways. Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay. This method has detected P. ramorum at scales ranging from small, intermittent seasonal drainages to the Garcia, Chetco, and South Fork Eel Rivers in California and Oregon (144, 352, and 689 mi2 drainage areas, respectively). It can detect the existence of infected plants in watersheds before any mortality from the infections becomes evident. Of course, it cannot detect the exact locations of those infected plants: at the first sign of P. ramorum propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.
A less technical means of detecting P. ramorum at the landscape level involves engaging local landowners across the landscape in the search. Many local county Agriculture Departments and University of California Cooperative Extension offices in California have been able to keep track of the distribution of the pathogen in their regions through reports and samples brought to them by the public. In 2008, the Garbelotto Laboratory at UC Berkeley, along with local collaborators, hosted a series of educational events, called “SOD Blitzes,” designed to give local landowners basic information about P. ramorum and how to identify its symptoms; each participant was provided with a sampling kit, sampled a certain number of trees on his or her property, and returned the samples to the lab for analysis. It is hoped that this kind of “citizen science” can help generate an improved map of P. ramorum distribution in the areas where the workshops are held.
Wildland management
The course that P. ramorum management should take depends on a number of factors, including the scale of the landscape upon which one hopes to manage it. Management of P. ramorum has been undertaken at the landscape/ regional level in Oregon in the form of a campaign to completely eradicate the pathogen from the forests in which it has been found (mostly private, but also USDA Forest Service and USDI Bureau of Land ManagementBureau of Land Management
The Bureau of Land Management is an agency within the United States Department of the Interior which administers America's public lands, totaling approximately , or one-eighth of the landmass of the country. The BLM also manages of subsurface mineral estate underlying federal, state and private...
ownership). The eradication campaign involves vigorous early detection by airplane and watercourse monitoring, a U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) and Oregon Department of Agriculture-led quarantine
Quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....
to prevent movement of host materials out of the area where infected trees are found, and immediate removal of P. ramorum host vegetation, symptomatic or not, within a 300 feet (91.4 m) buffer around each infected tree.
The Oregon eradication effort, which began near the town of Brookings
Brookings, Oregon
Brookings is a city in Curry County, Oregon, United States. It was named after John E. Brookings, president of the Brookings Lumber and Box Company, which founded the city in 1908. As of the 2010 census the population was 6,336. The total population of the Brookings area is over 13,000, which...
in southwest Oregon in 2001, has adapted its management efforts over the years in response to new information about P. ramorum. For example, after inoculation trials of various tree species more clearly delineated which hosts are susceptible, the Oregon cooperators began leaving non-host species such as Douglas-fir and red alder on site. In another example, after finding that a small percentage of tanoak stumps that were resprouting on the host removal sites were infected with the pathogen—whether these infections were systemic or reached the sprouts from the surrounding environment is unknown—the cooperators began pretreating trees with very small, targeted amounts of herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
to kill the root systems of infected tanoaks before cutting them down. The effort has been successful in that while it has not yet completely eradicated the pathogen from Oregon forests, the epidemic in Oregon has not taken the explosive course that it has in California forests.
California, on the other hand, faces significant obstacles that preclude it from mounting the same kind of eradication effort. For one thing, the organism was too well established in forests in the Santa Cruz
Santa Cruz, California
Santa Cruz is the county seat and largest city of Santa Cruz County, California in the US. As of the 2010 U.S. Census, Santa Cruz had a total population of 59,946...
and San Francisco Bay
San Francisco Bay
San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...
areas by the time the cause of Sudden Oak Death was discovered to enable any eradication effort to succeed. Even in still relatively uninfested areas of the north coast and southern Big Sur
Big Sur
Big Sur is a sparsely populated region of the Central Coast of California where the Santa Lucia Mountains rise abruptly from the Pacific Ocean. The name "Big Sur" is derived from the original Spanish-language "el sur grande", meaning "the big south", or from "el país grande del sur", "the big...
, regionally coordinated efforts to manage the pathogen face huge challenges of leadership, coordination, and funding. Nevertheless, land managers are still working to coordinate efforts between states, counties, and agencies to provide P. ramorum management in a more comprehensive manner.
Several options exist for landowners who want to treat to limit the impacts of Sudden Oak Death on their properties. None of these options is foolproof, guaranteed to eradicate P. ramorum, or guaranteed to prevent a tree from becoming infected. Some are still in the initial stage of testing. Nevertheless, when used thoughtfully and thoroughly, some of the treatments do improve the likelihood of either slowing the spread of the pathogen or of limiting its impacts on trees or stands of trees. Assuming that the landowner has correctly identified the host tree(s) and symptom(s), has submitted a sample to a local authority to send to an approved laboratory for testing, and has received confirmation that the tree(s) are indeed infected with P. ramorum—or, alternatively, assuming that the landowner knows that P. ramorum-infected trees are nearby and wants to protect the resources on his or her property—he or she can attempt control by cultural (individual-tree), chemical, or silvicultural (stand-level) means.
The best evidence that cultural techniques might help protect trees against P. ramorum comes from research that has established a correlation between disease risk in coast live oak trees and the trees’ proximity to bay laurel. In particular, this research found that bay laurel trees growing within 5m of the trunk of an oak tree were the best predictors of disease risk. This implies that strategic removal of bay laurel trees near coast live oaks might decrease the risk of oak infection. Wholesale removal of bay laurel trees would not be warranted, since the bay laurels close to the oak trees appear to provide the greatest risk factor. Whether the same pattern is true for other oaks or tanoaks has yet to be established. Research on this subject has been started for tanoak, but any eventual cultural recommendations will be more complicated, because tanoak twigs also serve as sources of P. ramorum inoculum.
A promising treatment for preventing infection of individual oak and tanoak trees—not for curing an already established infection—is a phosphonate
Phosphonate
Phosphonates or phosphonic acids are organic compounds containing C-PO2 or C-PO2 groups . Bisphosphonates were first synthesized in 1897 by Von Baeyer and Hofmann. An example of such a bisphosphonate is HEDP . Since the work of Schwarzenbach in 1949, phosphonic acids are known as effective...
fungicide
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
marketed under the trade name Agri-fos. Phosphonate is a neutralized form of phosphorous acid that works not by direct antagonism of Phytophthora, but by stimulating various of kinds of immune responses on the part of the tree. It is mostly environmentally benign if not applied to non-target plants and can be applied either as an injection into the tree stem or as a spray to the bole. When applying Agri-fos as a spray, it must be combined with an organosilicate surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
, Pentra-bark, to enable the product to adhere to the bole long enough to be absorbed by the tree. Agri-fos has been very effective in preventing tree infections, but it must be applied when visible symptoms of P. ramorum on other trees in the immediate neighborhood are still relatively distant; otherwise, it is likely that the tree one wishes to treat is already infected but that visible symptoms have not yet developed (this is especially true for tanoak).
Trials of silvicultural methods for treating P. ramorum began in Humboldt County
Humboldt County, California
Humboldt County is a county in the U.S. state of California, located on the far North Coast 200 miles north of San Francisco. According to 2010 Census Data, the county’s population was 134,623...
in northwest coastal California in 2006. The trials have taken place on a variety of infested properties both private and public and have generally focused on varying levels and kinds of host removal. The largest (50 acres (202,343 m²)) and most replicated trials have involved removal of tanoak and bay laurel by chainsaw
Chainsaw
A chainsaw is a portable mechanical saw, powered by electricity, compressed air, hydraulic power, or most commonly a two-stroke engine...
throughout the infested stand, both with and without subsequent underburning designed to eliminate small seedlings and infested leaf litter. Other treatments included host removal in a modified “shaded fuelbreak” design in which all bay laurel is removed, but not all tanoaks; bay and tanoak removal using herbicides; and removal of bay laurel alone. The results of these treatments are still being monitored, but repeated sampling has so far detected only very small amounts of P. ramorum in the soil or on vegetation in the treated sites.
Nursery management
Research and development in managing P. ramorum in nursery settings extends from P. ramorum in the individual plant, to P. ramorum in the nursery environment, to the pathogen’s movement across state and national borders in infected plants.An array of studies have tested the curative and protective effects of various chemical compounds against P. ramorum in plants valued as ornamentals or Christmas trees. Many studies have focused on the four main ornamental hosts of P. ramorum (Rhododendron
Rhododendron
Rhododendron is a genus of over 1 000 species of woody plants in the heath family, most with showy flowers...
, Camellia
Camellia
Camellia, the camellias, is a genus of flowering plants in the family Theaceae. They are found in eastern and southern Asia, from the Himalaya east to Korea and Indonesia. There are 100–250 described species, with some controversy over the exact number...
, Viburnum
Viburnum
Viburnum is a genus of about 150–175 species of shrubs or small trees in the moschatel family, Adoxaceae. Its current classification is based on molecular phylogeny...
, and Pieris
Pieris
Pieris can refer to:Organisms* Pieris is the andromeda or fetterbush genus in the plant family Ericaceae* Pieris , described by Franz Paula von Schrank in 1801, is the garden white genus in the butterfly family Pieridae...
). Several effective compounds have been found; some of the most effective include mefenoxam, metalaxyl
Metalaxyl
Metalaxyl is a phenylamide fungicide with systemic function. Its chemical name is methyl N--N--DL-alaninate. It can be used to control Pythium in a number of vegetable crops, and Phytophthora in peas....
, dimethomorph, and fenamidone
Fenamidone
Fenamidone is a foliar fungicide used on grapes, ornamentals, potatoes, tobacco, and vegetables. It exerts its fungicidal effects by acting as a Qo inhibitor....
. Many of these studies have converged upon the following conclusions: chemical compounds are, in general, more effective as preventatives than in curatives; when used preventatively, chemical compounds must be reapplied at various intervals; and chemical compounds can mask the symptoms of P. ramorum infection in the host plant, potentially interfering with inspections for quarantine efforts. In general, these compounds suppress but do not eradicate the pathogen, and some researchers are concerned that with repeated use the pathogen may become resistant to them. These studies and conclusions are summarized by Kliejunas.
Another area of research and evolving practice deals with eliminating P. ramorum from nursery environments in which it is established to prevent human-mediated pathogen movement within the ornamental plant trade. One way of approaching this is through a robust quarantine and inspection program, which the various federal and state regulatory agencies have implemented. Under the federal P. ramorum quarantine program implemented by USDA APHIS
Aphis
Aphis may refer to:* Aphis, a genus of aphid species* Animal and Plant Health Inspection Service , organizational unit of the USDA* HMS Aphis , Royal Navy insect class gunboat...
, nurseries in California, Oregon, and Washington are regulated and must participate in an annual inspection regime; nurseries in the fourteen infested counties in coastal California, plus the limited infested area in Curry County
Curry County, Oregon
Curry County is a county located in the U.S. state of Oregon. In 2010, its population was 22,364. The county is named for George Law Curry, a governor of the Oregon Territory. The seat of the county is Gold Beach.-Economy:...
, Oregon, must participate in a more stringent inspection schedule when shipping out of this area.
Much of the research into disinfesting nurseries has focused on the voluntary Best Management Practices (BMPs) that nurseries can implement to prevent P. ramorum’s introduction into the nursery and movement from plant to plant. In 2008, a group of nursery industry organizations issued a list of BMPs that includes subsections on Pest Prevention/Management, Training, Internal/External Monitoring/Audits, Records/Traceability, and Documentation. The document includes such specific recommendations as “Avoid overhead irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
of high-risk plants”; “After every crop rotation
Crop rotation
Crop rotation is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons.Crop rotation confers various benefits to the soil. A traditional element of crop rotation is the replenishment of nitrogen through the use of green manure in sequence with cereals...
, disinfect propagation
Plant propagation
Plant propagation is the process of creating new plants from a variety of sources: seeds, cuttings, bulbs and other plant parts. Plant propagation can also refer to the artificial or natural dispersal of plants.-Sexual propagation :...
mist beds, sorting area, cutting benches, machines and tools to minimize the spread or introduction of pathogens”; and “Nursery personnel should attend one or more P. ramorum trainings conducted by qualified personnel or document self-training”.
Research on control of P. ramorum in nurseries has also focused on disinfesting irrigation water containing P. ramorum inoculum. Irrigation water can become infested from bay trees in the forest (if the irrigation source is a stream), from bay trees overhanging irrigation ponds, from runoff from infested forests, or from recirculated irrigation water. Experiments in Germany with three types of filters—slow sand filters, lava filter
Lava filter
A lava filter is a biological filter that uses lavastone pebbles as support material on which microorganisms can grow in a thin biofilm. This community of microorganisms, known as the periphyton break down the odor components in the air, such as hydrogen sulfide. The biodegradation processes that...
s, and constructed wetlands—showed that the first two removed P. ramorum from the irrigation water completely, while 37% of the post-treatment water samples from the constructed wetland still contained P. ramorum.
Since P. ramorum can persist for an undetermined period of time within the soil profile, management programs in nurseries should also deal with delineating the pathogen’s distribution in nursery soil and eliminating it from infested areas. A variety of chemical options have been tested for soil disinfestation, including such chemicals as chloropicrin
Chloropicrin
Chloropicrin, also known as PS, is a chemical compound with the structural formula Cl3CNO2. This colourless highly toxic liquid was once used in chemical warfare and is currently used as a fumigant and nematocide.-History:...
, metham sodium
Metham sodium
Metham sodium is a soil fumigant used as a pesticide, herbicide, and fungicide. It is one of the most widely used pesticides in the United States, with approximately 60 million pounds used in 2001...
, iodomethane
Iodomethane
Methyl iodide, also called iodomethane, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hydrogen atom by an atom of iodine. It is naturally...
and dazomet. Lab tests indicated that all of these chemicals were effective when applied to infested soil in glass jars. Additionally, tests on volunteer nurseries with infested soil demonstrated that dazomet (trade name Basamid) fumigation followed by a 14-day tarping period successfully removed P. ramorum from the soil profile. Other soil disinfestation practices under investigation, or in which interest has been expressed, include steam sterilization
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...
, solarization
Soil solarization
Soil solarization is an environmentally friendly method of using solar power for controlling disease agents in the soil by mulching the soil and covering it with tarp, usually with a transparent polyethylene cover, to trap solar energy....
, and paving of infested areas.
General sanitation in infested areas
One of the most important aspects of P. ramorum control involves interrupting the human-mediated movement of the pathogen by ensuring that infested materials do not move from location to location. While enforceable quarantines perform part of this function, basic cleanliness when working or recreating in infested areas is also important. In most cases, cleanliness practices involve ridding potentially infested surfaces—such as shoes, vehicles, and pets—of foliage and mud before leaving the infested area. The demands of implementing these practices become more complex when large numbers of people are working in infested areas, as in construction, timber harvesting, or wildfire suppression. The California Department of Forestry and Fire ProtectionCalifornia Department of Forestry and Fire Protection
The California Department of Forestry and Fire Protection is the State of California's agency responsible for fire protection in State Responsibility Areas of California as well as the administration of the state's private and public forests. It is often referred to as The California Department of...
and USDA Forest Service have implemented guidelines and mitigation requirements for the latter two situations; basic information about cleanliness in P. ramorum-infested areas can be found at the California Oak Mortality Task Force web site (www.suddenoakdeath.org) under the “Treatment and Management” section (subsection “Sanitation and Reducing Spread”).
Government Agency Involvement
In EnglandEngland
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 2009, the Forestry Commission
Forestry Commission
The Forestry Commission is a non-ministerial government department responsible for forestry in Great Britain. Its mission is to protect and expand Britain's forests and woodlands and increase their value to society and the environment....
, DEFRA, the Food and Environment Research Agency
Food and Environment Research Agency
The Food and Environment Research Agency, a new Defra executive agency was vested on 1 April 2009.-History:The agency was formed by bringing together the Central Science Laboratory at Sand Hutton, the Plant Health Division / Plant Health and Seeds Inspectorate in York, the Plant Variety Rights...
, Cornwall County Council
Cornwall County Council
Cornwall Council is the unitary authority for Cornwall, in England, United Kingdom. The council, and its predecessor Cornwall County Council, has a tradition of large groups of independents, having been controlled by independents in the 1970s and 1980s...
, and Natural England
Natural England
Natural England is the non-departmental public body of the UK government responsible for ensuring that England's natural environment, including its land, flora and fauna, freshwater and marine environments, geology and soils, are protected and improved...
are working together to record the locations and deal with this disease. Natural England
Natural England
Natural England is the non-departmental public body of the UK government responsible for ensuring that England's natural environment, including its land, flora and fauna, freshwater and marine environments, geology and soils, are protected and improved...
is offering grant funding through its Environmental Stewardship
Environmental Stewardship
Environmental Stewardship is an agri-environment scheme run by the Department for Environment, Food and Rural Affairs in England. It was formally launched on 18 March 2005, although the first agreements did not start until 1 August 2005....
, Countryside Stewardship and Environmentally Sensitive Area
Environmentally Sensitive Area
An Environmentally Sensitive Area is a type of designation for an agricultural area which needs special protection because of its landscape, wildlife or historical value. The scheme was introduced in 1987...
schemes to clear rhododendron. In 2011, the Forestry Commission
Forestry Commission
The Forestry Commission is a non-ministerial government department responsible for forestry in Great Britain. Its mission is to protect and expand Britain's forests and woodlands and increase their value to society and the environment....
started felling 10000 acres (40.5 km²) of larch
Larch
Larches are conifers in the genus Larix, in the family Pinaceae. Growing from 15 to 50m tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south...
forest in the SW of England, as an attempt to halt the spread of the disease.
External links
- http://www.suddenoakdeath.org
- New Scientist news
- University of California SOD pest notes
- California Agriculture
- UK Department of Environment, Food and Rural Affairs - Phytophthora Ramorum Factsheet
- Washington State University SOD Program
- Reducing spread of SOD
- Sudden Oak Death Center for Invasive Species Research
- Species Profile- Sudden Oak Death (Phytophthora ramorum), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Sudden Oak Death.