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
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
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.
Regional Infestation Map