Extension Report: Redbay wilt; Invasive pests moving toward Alabama
The redbay ambrosia beetle (Xyleborus glabratus) is a relatively new imported pest that is impacting trees in the Lauraceae family in the Southeastern United States. This beetle feeds on the woody tissues of host trees and introduces a fungus that it carries, causing redbay wilt. Common trees likely to be impacted in Alabama and the Gulf Coast are redbay (P. borbonia), swampbay (P. palustris), sassafras (Sassafras albidum) and in Florida Avocado (P. Americana).
The ambrosia beetle while reportedly not in Alabama has caused tree mortality along the Atlantic coast of Florida, Georgia, and North Carolina and most recently in Jackson County, Mississippi (which neighbors Mobile County). The greatest economic impacts of this pest are to the avocado crops in Florida, however, in Alabama there are likely to be some ecological impacts.
Invading pests pose a major threat to Alabama’s natural ecosystems. Whether they are plants, animals or insects the damage they cause can have significant impacts to the native flora and fauna. The challenges associated with invading insects are the lack of natural predators to control their populations. Additionally, their hosts or trees they impact have few natural defenses due to the pest not being a natural component of the ecosystem. This combination can result in large pest populations causing significant mortality of host species.
In the Northeast and Midwest the introduction of the Emerald Ash borer and Asian Longhorn Beetle, both invasive pests, have cause the mortality of thousand of ash and maple trees. Entire neighborhoods have been decimated when urban forests, primarily comprised of ash trees, were removed due to infestation of emerald ash borers.
While trees in the Lauraceae family are not prominent urban trees, they do comprise a significant part of Alabama’s forest ecosystem. Redbay and other trees in the Lauraceae family are of ecological importance to deer that browse on leaves and quail, turkey, songbirds and bears that feed on their fruit. Additionally, there are various insects that depend on redbay, such as the swallowtail butterfly (Papilio palamedes), to complete their life cycle. Economically the impact is relatively minimal in Alabama as the tree is used, to some degree, in cabinets, boat manufacturing, packing materials and veneer. However, the economic impacts associated to cities and parks that may have to remove, dispose and replace lost trees could be more significant.
The redbay ambrosia beetle was likely introduced in wooden packing material arriving from Southeast Asia. The native range of the redbay ambrosia beetle is India, Japan, Myanmar, and Taiwan. Adult beetles are a brown black color, long and cylindrical in shape, and roughly two millimeters long. Identifying these beetles and the larva are difficult and a specialist should be consulted. In most cases it is easier to identify symptoms and damage associated with the pest rather than the insect.
Symptoms and damage identification
Redbay ambrosia beetle feeding on host trees is seldom enough to kill the tree. The redbay wilt, associated with the redbay ambrosia beetle is actually a fungus that the beetle introduce when feeding on the tree. These beetles have a symbiotic relationship with the fungus Raffaelea lauricola that is introduced into the sapwood clogging the vessel system in the tree. The vessels, which transport sugars and water, are essential to maintain growth within trees. Once clogged by this fungus the leaves will begin to wilt and eventually turn a reddish or purplish color. This wilting and discoloration may initially only be limited to a few branches but will eventually spread to the entire tree. Over time all the leaves will turn brown and can stay attached to the tree for up to one year. When bark is removed on wilted trees it is common to see a bluish to dark black discoloration in the outer sapwood that runs with the grain of the wood.
Additionally, trees infested with redbay ambrosia beetle are identifiable by the toothpick-like structures composed of sawdust emerging from the trunk of the tree. The toothpick-like structures are sawdust or beetle frass that are being pushed from the feeding holes. If a tree is found with both the toothpick-like structures and the blue stain on the wood, it is very likely the tree has been infested by redbay ambrosia beetle and should be reported to the Alabama Cooperative Extension System.
Spread of the redbay ambrosia beetle
Since the identification of redbay wilt in three Georgia and South Carolina counties in 2004, the disease has spread to at an estimated 60 counties by 2009. The beetles are known to fly up to a few kilometers and can even travel further with strong wind currents to infest new trees. However, the primary way this beetle is being spread is through the transportation of wood products by humans. Efforts need to be made to stop moving firewood, wood chips for BBQ’s, mulches, wood packing materials or any other lauraceau wood products from known infested areas. The transportation of infested wood products is known to be a major contributor to the spread of the redbay ambrosia beetle in the southeast.
Mitigation and response to redbay laurel wilt
The redbay ambrosia beetle and the associated fungus that cause redbay wilt are well established in a 60,000 square mile area of Florida, Georgia, South Carolina and Mississippi. Eradicating the insect is not feasible in the southeast. The reality is that there are likely to be high rates of host tree mortality throughout the Southeast as this insect continues to spread. The easiest way to prevent the spread and contain this potentially devastating pest is by restricting the transport of infested wood products.
While chemical control in natural forest is not feasible for environmental and economic reasons, for individual urban trees there are some preventative measures. Research by the Bartlett Tree Labs in North Carolina has shown some success in preventing healthy trees from being infected. The macro-infusion or injection of redbay trees with the fungicide propiconazole has shown to prevent the trees from being infested for up to one year. However, reapplying the treatment is necessary for consecutive years. This treatment is costly and will often require using a certified arborist as it is relatively specialized and labor intensive.
It is important to note that while the redbay ambrosia beetle and its associated fungus have not been identified in Alabama, the public should report any of the above symptoms in redbay trees to the Alabama Cooperative Extension System. The hope is that this pest does not reach Alabama, however, with the proximity of the sitting in Jackson County, Miss., it is likely that this pest will occur in Alabama in the next few years.
This article is not suggesting that homeowners begin preventative chemical control treatments, but rather that they become familiar with identifying redbay, swamp redbay and sassafras trees and keep a keen eye for any of the above symptoms and damage in these tree species. If this damage should be sited in south Alabama please contact your local Extension office and report the incidence.
(Beau Brodbeck is a county extension agent with the Baldwin County office, Alabama Cooperative Extension System. He may be reached at 251-937-7176, 251-943-5061 or 251-928-0860, ext. 2222 or email: email@example.com.)
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