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The following section was extracted from Recovery plan for laurel wilt on redbay and other forest species. Caused by Raffaelea lauricola , vector Xyleborus glabratus ( Mayfield et al. 2009).
Limit transport of infested/infected host material
Efforts to prevent the long-distance, human-assisted spread of the RAB and laurel wilt pathogen could help delay the onset of laurel wilt impacts in currently unaffected areas, possibly allowing more time for new management tactics to be developed. Limitations on long-distance dispersal could include:
In many forests and other natural areas with a redbay component, the most reasonable management response after laurel wilt is established may be to simply let the disease run its course.
As yet, there are no proven silvicultural or arboricultural treatments for mitigating the impact of laurel wilt. One attempt to eradicate the vector and pathogen from a local area through sanitation removal/destruction of RAB-infested trees was not successful. When laurel wilt was first detected on Jekyll Island, GA in 2006, the Georgia Forestry Commission (GFC) with cooperation from the Jekyll Island Authority deployed a chainsaw strike team and removed all known symptomatic redbays (more than 400 trees) from residential and natural areas and burned them at a central location. Nonetheless, by late 2007 laurel wilt was found throughout the island (James Johnson, GFC, unpublished presentation). This underfunded eradication attempt suggests that sanitation removal of only symptomatic host material is not an effective means of mitigating the impacts of laurel wilt during an epidemic. The tactic might be more fruitful if all host trees large enough for brood production by RAB are removed, if the sanitation is augmented by protection of individual trees with pesticides (see below), and/or if applied at a time when RAB populations, disease incidence, and host abundance in the landscape are very low. A solid commitment of funds and personnel to do follow-up surveys and complete removal of brood material in a timely fashion would be necessary for long-term success with sanitation. In addition, sanitation might be used to in conjunction with mass trapping (see below) to reduce RAB populations in defined areas. At the time of the Jekyll Island trial an effective lure had not been developed.
Although eradication attempts in the currently-infested areas of the southeastern Atlantic Coastal Plain appear fruitless, spread of the vector and pathogen into new areas might be slowed by prevention of long-distance spread by human activities, and possibly by rigorous, sanitation programs aimed at suppressing laurel wilt at outlier locations. Such sanitation efforts at or beyond the leading edge of the known laurel wilt range, however, would probably only be successful where host trees are relatively scattered and could be surveyed repeatedly throughout the year, where the disease and vector have not been present for very long, and where there is a full, long-term commitment (both financially and administratively) of involved agencies and stakeholders.
Although the pathogen has not been documented to spread by any means other than the beetle vector, arborists and tree-service professionals should consider cleaning/sterilizing saws and pruning blades after cutting an infected tree and before using them on uninfected lauraceous tree species. The potential for transmission of laurel wilt by pruning tools is currently being investigated by researchers at the University of Florida. Tree-service and utility pruning crews should be careful not to transport RAB-infested host material over long distances on chipping equipment or in chip vans.
At one site in Florida, macro-infusion of redbay trees with the fungicide propiconazole was demonstrated to protect healthy redbay trees from development of laurel wilt after artificial inoculation with the pathogen (Mayfield et al. 2008a). Continued monitoring of trees in that study into 2009 suggests that the treatment, properly applied, can protect redbay trees for at least a year, but probably not for 2 or more years (A.E. Mayfield III, unpublished data). The macro-infusion process, which has also been used to protect against vascular wilt diseases in other species (e.g., oaks and elms), is relatively labor intensive and expensive, so it is impractical to implement on a large scale. It is currently unknown whether repeated use of this treatment can successfully protect a redbay tree through the duration of a laurel wilt epidemic, and if so, how many times a tree can or should be treated before the treatments can be discontinued (if at all). Recent data suggest RAB populations remain relatively high for 7-8 years following initial discovery until they fall to very low levels after the redbay population is gone (J.L. Hanula, unpublished). Treatment of symptomatic trees has not been evaluated and is not recommended. Nonetheless, propiconazole macro-infusion may be an option for protecting individual, high-value, landscape redbay trees, at least in the short-term. Removal of diseased redbay or other host material from the immediate area around the treated tree may help reduce the possibility of RAB attacks. Research may eventually demonstrate the efficacy of other fungicides, insecticides, or methods of delivery against RAB and the laurel wilt pathogen. Because RAB populations thus far have continued at very low levels even when all apparent host material is dead, individually treated trees may need to be protected in perpetuity.
Manuka oil is as attractive to RAB as freshly cut redbay wood (Hanula and Sullivan 2008), and healthy, unwounded redbay trees are somewhat less attractive than wounded trees (Hanula et al. 2008). Although not yet demonstrated, protecting healthy trees by drawing RAB away from them may be possible. Combining manuka oil with other potential attractants in traps, or combining it with an insecticide and applying the combination to non-host substrates, may be effective ways to help minimize RAB populations within limited areas such as parks, neighborhoods or barrier islands. These techniques might be used to eradicate low-level RAB populations from isolated areas such as barrier islands after laurel wilt has eliminated most mature redbay trees. Mass trapping could be tested in combination with sanitation and chemical control to protect redbay trees that survive the initial wave of mortality.
Seed collection is routinely used as a means to preserve the genetic diversity of a plant species. Although seed of many species can be dried, stored below 0o C and remain viable for many years, long-term seed storage does not seem feasible for redbay. Due to their high lipid content, seeds of species in the Lauraceae are generally temperature recalcitrant, meaning it is difficult or impossible to sufficiently reduce the moisture content of the seed for storage at sub-freezing temperatures without killing the seed.
A protocol for collecting and submitting redbay seed to the USDA Forest Service National Seed Lab (NSL) in Dry Branch, GA was initiated in the summer of 2007 to determine the length of time redbay seed could be stored and to serve as a short-term storage facility for seed collected from impacted or potentially impacted areas.
Because long-term seed storage using traditional methods is not an option, other alternatives have been discussed. Cryopreservation of embryos from seeds has been identified as a possible option, but is expensive and labor intensive to implement on a large scale. Ex situ conservation of trees outside the southeastern Atlantic Coastal Plain region is another possibility, but that would require funding and a coordinated effort among organizations from across the region. More survey and impact data on species like sassafras, pondspice and pondberry would also be needed to help support and justify ex situ conservation programs for laurel wilt hosts. Because long-term germplasm preservation of these species is unlikely without an extensive outlay of money and resources, it would seem necessary to first demonstrate some likelihood of re-establishment success of host plant species into laurel wilt-impacted areas. The persistence of low-level RAB populations on places like Hilton Head Island (where the laurel wilt epidemic has already run its course) currently calls this likelihood into question.
Jason Smith (University of Florida) and colleagues are investigating the possibility of natural resistance to laurel wilt in redbay populations. Research has included identifying and taking cuttings from putatively resistant redbays (mature trees that have remained alive in areas heavily impacted by laurel wilt), rooting them, and growing them to a size where they can be evaluated for disease susceptibility. Though laurel-wilt resistant redbays are not yet known, research may lead to their availability and use in the future.
An integrated management strategy is needed to limit the spread and impact of laurel wilt. This strategy may take various forms depending on the area of interest. In many forests and other natural areas with a redbay component, the most reasonable management response where laurel wilt is established may be to simply let the disease run its course. “Recovery” from laurel wilt in redbay and other forest species could be considered in terms of the following general courses of action:
USDA Forest Service - Forest Health Protection, Southern