Is there treatment for phytophthora ramorum?
589513#41
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 () 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.
Phytophthora ramorum
589513#33
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.
Phytophthora ramorum
589513#25
Early detection of "P. ramorum" is essential for its control. On an individual-tree basis, preventive 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.
Phytophthora ramorum
589513#46
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 filters, 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".
Phytophthora ramorum
589513#27
Because of these difficulties, researchers have developed some other approaches for identifying "P. ramorum". The enzyme-linked immunosorbent assay test can be the first step in nonculture 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 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 likely positive samples 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".
Phytophthora ramorum
589513#38
Several options exist for landowners who want to limit the impacts of SOD 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.
Phytophthora ramorum
589513#19
Species of "Phytophthora" 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 outcompete their parent species. Thus, "P, ramorum" is possibly a hybrid between two species. Its unique morphology does support this. Also, three sequences studied to establish the phylogeny of "Phytophthora": ITS, cox II and nad 5, were identical, supporting "P. ramorum" having recently evolved.
Phytophthora ramorum
589513#42
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.
Phytophthora ramorum
589513#40
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 kinds of immune responses on the part of the tree. It is mostly environmentally benign if not applied to nontarget 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, the tree to be treated likely is already infected, but visible symptoms have not yet developed (especially true for tanoak).
Phytophthora ramorum
589513#0
Phytophthora ramorum is the oomycete plant pathogen known to cause the disease sudden oak death (SOD). The disease kills oak and other species of trees and has had devastating effects on the oak populations in California and Oregon, as well as being present in Europe. Symptoms include bleeding cankers on the tree's trunk and dieback of the foliage, in many cases eventually leading to the death of the tree.
Phytophthora ramorum