Alabama's Forests are Being Threatened by Three New Pests


During the latter part of July 2010, separate news updates were released to the southeastern states proclaiming the rapid spread of three specific destructive pests. On July 27, a pest alert was immediately released announcing the discovery of thousand cankers disease in East Tennessee. On that same day, a second media release reported the presence of emerald ash borer in Knox County, also in Tennessee. The following day, July 28, a professor of entomology from Mississippi State University sent a warning to Alabama declaring that laurel wilt disease is rapidly approaching the state line.

The initial response to this news for Alabama was panic, but specific actions can be done to prepare for this possible threat to our native trees. We have the opportunity to begin monitoring targeted forest areas for detection of these three new pests. The Early Detection and Rapid Response protocol is established for this particular purpose, a proactive approach for identifying, locating, and controlling invasive pests.

Thousand Cankers Disease
The thousand cankers disease causes dieback and mortality of eastern black walnut trees. An insect-disease complex that normally only occurs in the western states, it was documented for the first time in the Southeast. In a residential area near Knoxville, Tennessee, five symptomatic eastern black walnut (Juglans nigra) trees were tested positive for the walnut twig beetle (Pityophthorus juglandis) and its associated fungus (Geosmithia morbida). Later in August, a second round of sampling was done at different sites near Knoxville for further confirmation of this pest. Based on the results, the thousand cankers disease has been in Tennessee, in more than one area, for longer than previously suspected.

Generally, individual landowners may believe that their declining walnut trees are suffering from drought-related problems, since the early symptoms resemble that of drought stress. Specific symptoms include yellowing of foliage, cankers on branches, exit/entrance insect holes on branches, and eventually, the mortality of the tree. The first apparent symptoms are the yellowing of the foliage. Later, the foliage becomes brown and wilted.

The bark surface generally has no symptoms, but under close analysis, numerous entrance and exit holes are present on dying branches. The walnut twig beetle creates galleries in the phloem while vectoring the deadly fungus. The fungus causes cankers on infected branches, resulting in some cracking of the bark. Finally, dieback of the branch occurs from the attack. The walnut tree finally succumbs from the attack within two or three years.

No one is exactly sure how this pest spread from the western U.S. (Washington, Oregon, California, Idaho, Utah, Arizona, Colorado, and New Mexico) into Tennessee, by-passing all of the other states. However, transportation of firewood is the main hypothesis of this pest introduction. Because the beetle is classified as native, quarantines are difficult to establish. Since the fungus is relatively new, perhaps it will be classified as non-native. The Tennessee Department of Agriculture plans to issue a quarantine in Knox County prohibiting the movement of firewood, black walnut nursery stock, and other materials that can spread the thousand cankers disease.


7. Forestry and Natural Resource Webinar Series on September 3, 2010

Emerald Ash Borer
Also in East Tennessee, an emerald ash borer (Agrilus planipennis) infestation was detected at a truck stop in Knox County. After receiving the report of a possible find, state and federal officials collected specimens of infected ash logs and sent them to the U.S. Department of Agriculture for positive identification. The samples confirmed that emerald ash borer is now present in Tennessee.

Imported from Asia, this insect was positively identified in 2002. Since the initial introduction into the U.S. in the Detroit, Michigan area from wood packing material, the emerald ash borer has rapidly spread into Illinois, Indiana, Iowa, Kentucky, Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Virginia, West Virginia, and Wisconsin, attacking and killing ash trees (Fraxinus spp.).

Initial attack is difficult to detect, since damage to infested trees may not be immediately apparent. Damage is caused by the larvae of this exotic insect, creating galleries and feeding in the phloem underneath the bark. This girdling activity disrupts water and nutrient flow. Infested trees will exhibit branch dieback in the upper crown, excessive epicormic branching on the tree trunk, and vertical bark split. By the time these symptoms are recognized, the infestation is spreading to other ash trees. Infested trees will succumb from the attack within two or three years.

In response to this breaking report, the Tennessee Department of Agriculture plans to issue a quarantine in Knox and Loudoun counties prohibiting the movement of firewood, ash nursery stock, and other materials that can spread the emerald ash borer. The agency will also have plant inspectors and professional foresters conduct a thorough survey of ash trees in the area to assess the extent of the infestation. Since this pest is non-native, the USDA Animal and Plant Health Inspection Service is expected to issue a federal quarantine later supporting national efforts to control this invasive, destructive pest.


Laurel Wilt Disease
The last breaking news sent to Alabama was about an insect-disease complex that is threatening Alabama’s southern border. From survey traps and observation conducted in Jackson County, Mississippi, several symptomatic camphor (Cinnamomum camphora) and redbay (Persea borbonia) trees were found to be infected by laurel wilt disease. Also recently documented in Mississippi was the first symptomatic sassafras (Sassafras albidum) tree succumbing to this insect-disease complex. Because of recent reports of declining redbay trees in Alabama, two survey traps were placed just across the state line in Mobile County.

Another import from Asia, the redbay ambrosia beetle (Xyleborus glabratus) was first detected in a survey trap in Port Wentworth, Georgia in 2002. Since its initial introduction from infested solid wood packing materials, it has spread to redbay trees in eastern Georgia and South Carolina. By 2005, this insect-disease complex was discovered in Florida. In July 2009, declining redbay trees were documented in Jackson County, Mississippi due to this non-native, invasive pest.

Trees of the laurel family (Lauraceae) are very susceptible to this insect-disease complex. Not only are redbay, camphor, and sassafras trees vulnerable, but also swamp bay (Perseapalustris), spicebush (Lindera melissifolia), pondspice (Litsea aestivalis), and avocado (Persea americana) can become potential hosts.

Difficult to detect at first, infected trees will soon display wilting leaves that appear red or purple in color. Part of the crown will show these symptoms, and eventually the entire crown will have wilted reddish foliage. This ambrosia beetle, unlike most, attacks healthy trees. The attack from the beetle does not necessarily kill the tree; it is the associated fungus (Raffaelea lauricola) that causes the damage. The insect vectors the fungus, inoculating the gallery walls as it creates these tunnels in the sapwood. The fungus clogs the vascular system of the tree, preventing the flow of water. The fungus also causes brown-to-black streaks in the sapwood. In the final stages of decline, ambrosia beetles will attack in large numbers, creating compacted sawdust that protrudes from the boring holes. Infested trees finally succumb to attack within one or two years.

Fortunately, the symptomatic redbay trees detected in Alabama were negative of laurel wilt disease, but the state was not completely “out of the woods”. In October of 2010, two beetle specimens were collected from one of the traps located in Mobile County, Alabama just north of Grand Bay. Later, these specimens were positively identified by Dr. John Riggins of Mississippi State University and USDA APHIS as redbay ambrosia beetles. The positive identification of these specimens made this the first confirmation of the redbay ambrosia beetle to exist in Alabama.

Additional Resources:

Laurel Wilt Regional Infestation Map