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A redbay at the NC Botanical Garden ©
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Besides the near extermination of ashes
and possibly other trees by the emerald ash borer, the subject of a
previous post (April 16, 2016), there are a few other serious non-native threats to the integrity
of North Carolina's environment, either established in nearby states
or already found here (there is an overview at:
ncforestservice.gov/forest_health/current_concerns.htm ). Another
major threat to forest ecosystems is laurel wilt, a non-native fungal
disease spread by the similarly exotic redbay ambrosia beetle, which
kills trees in the laurel family, especially redbays, but also
sassafras, avocados, and other species, and is already spreading in
southeastern North Carolina.
In summer 2002 a USDA pilot project to
detect newly arrived non-native insects, started only in 2001, caught
redbay ambrosia beetles (Xyleborus glabratus) around Port
Wentworth, Georgia, near Savannah. These tiny woodboring beetles,
about 2 mm long, are native from eastern India and Bangladesh to
Taiwan, southern Japan, and some Pacific islands, and are not a major
pest there. Females were trapped in 2002, probably the first
generation born in solid wooden packing material from Asia. It only
takes one female to start an infestation and the beetles can complete
their life cycle in as little as
40-60 days. There are multiple broods in a year and adults are
around at any time of year and the winged females are most active
late in the day, which is important when using some insecticides.
By 2003 people realized that an unusual number of redbay trees were
dying in Chatham County, Georgia (where Port Wentworth is located)
and across the border in Beaufort and Jasper counties in South
Carolina, and late in 2004 the cause was identified. Redbay ambrosia
beetles tunnel into living trees, inoculating them with various fungi
(what the beetles actually live off of), carried in pouches on the
beetles' mandibles. Apparently the non-native fungus Raffaelea
lauricola is what causes laurel
wilt. R. lauricola
spreads through a tree's xylem vessels, and the fungus itself and
possibly the tree's over zealous response to the infection cuts off
circulation, girdling and killing the aboveground parts of the tree
over as little as 3-12 weeks. Redbay ambrosia beetles have been
found carrying R. lauricola
in Asia, but laurel family trees there must have co-evolved with the
disease while it is a new epidemic in the Americas and can kill
healthy trees. The beetles prefer large trees, mostly boring into
the first 1.5 meters of the trunk, and sometimes it is possible to
see tiny “sawdust toothpicks” marking the boreholes. Older trees
are most at risk, but even saplings only 1 to 1.5 cm wide aren't
safe. In one place in Florida redbays 1” wide or more were
monitored and mortality rose from 10% to 92% in only 15 months and
mortality was 98% between 2004 and 2009 on St Catherines Island,
Georgia. The beetles prefer redbays (Persea borbonia)
here, but have been found on non-laurels in Asia. R.
lauricola has been found in live
oaks, but only laurel family trees are thought to be at risk, and the
fungus can be picked up and transmitted by other species of ambrosia
beetle in the laboratory. There is some evidence that avocados might
be getting laurel wilt from a different beetle.
Redbay is most at risk, but swamp bays (Persea palustris) and sassafras (Sassafras albidum) are also susceptible, as are two endangered small trees, pondberry (Lindera melissifolia) and pondspice (Litsea aestivalis). In experiments, Northern spicebush (Lindera benzoin), lancewood (Nectandra coriacea), and pepperleaf sweetwood/Gulf Licaria (Licaria triandra) can get laurel wilt to some degree and these small trees/bushes grow in areas already effected by the disease, but redbay ambrosia beetles prefer trees with thicker stems. Spicebush, which grows near waterways in the Triangle, apparently does not attract the beetles, so it may be at low risk, but the beetle likes Asian spicebush. Pepperleaf sweetwood is a Federal endangered species with fewer than 12 wild trees in Miami-Dade County, Florida, but it also grows on some Caribbean islands. By 2007 avocados (P. americana) were dying in yards in Jacksonville, Florida and in 2012 laurel wilt reached commercial groves in Miami-Dade County. The West Indian variety of avocado most common in Florida also happens to be the variety most susceptible to laurel wilt, and avocados are Florida's second biggest fruit industry. On the other hand, avocados on Merritt Island, Florida were surrounded by dying redbays for 3-4 years without major problems, and the beetles reproduce poorly in avocados. A fungus carried by a different ambrosia beetle is impacting avocados in California and affects over 200 plant species, but so far it is only a Western problem. In 2013 a bay laurel, an ornamental native to the Mediterranean, growing near an infected avocado in Gainesville, Florida was killed. Tests show that redbay ambrosia beetles are attracted to and can reproduce in California laurel (Umbellularia californica), and it is susceptible to laurel wilt if the disease gets to the West. Like redbay, California laurel is valued for woodworking, which makes human spread more likely. There is a Mexican redbay that is susceptible in the lab, and there are many related trees in Latin America, some important for timber. Bay laurel and viñátigo (P. indica), a common tree in Madeira and the Canary Islands, are susceptible. Ornamental camphortrees (Cinnamomum camphora) can be killed by laurel wilt, but they co-evolved with the redbay ambrosia beetle in Asia and aren't in much danger. In Asia the beetle is found in trees like Asian spicebush (Lindera latifolia), yellow Litsea (Litsea elongata), and sal (Shorea robusta), and is not known as a pest of avocados.
Sassafras
grows throughout North Carolina, while redbay is found in the Coastal
Plain, including Moore, Lee, Harnett, Johnston, and Wilson counties
just south and east of the Triangle. There are some redbays growing
behind the NC Botanical Garden's Totten Center, resembling more
familiar broadleaved evergreen magnolias. Spicebush is also found
throughout the state, but less so in the Coastal Plain. Pondspice
grows in a few places in southeastern NC and pondberry grows in and
around Bladen County, the epicenter of laurel wilt in southeast NC.
A single female
beetle is all it takes to start an infestation, and they can travel
about 15-34 miles (55 km) a year, and might also be carried in the
wind, but they are spreading furthest through unwitting human
transportation. In 2004 laurel wilt spread to a campground at
Stephen C Foster State Park in Georgia, west of the Okefeenokee
National Wildlife Refuge, probably with human help, and in 2007 it
spread around a hardwood mulch producer close to Nahunta, Georgia.
Earlier in 2006 an infestation started on a railroad line in Jesup,
Georgia near a pulp plant and state prison, either on its own or with
human help (see the Georgia Forestry Commission's Distribution and
Spread of Laurel Wilt Disease in Georgia: 2006-08 Survey and Field
Observations, 2008). In 2009 it spread to Richmond County,
Georgia, 65 km from the nearest known infestation (Evaluation of
Laurel Wilt Disease in Georgia: Progression in Redbay and Sassafras
- 2008-2010). The NC Forest Service hasn't disseminated
information this detailed about how laurel wilt is being spread, but
might if asked. Logs brought in for woodturning took the beetle to
Volusia County, Florida in 2008. It has been suggested that emerald
ash borers are using vehicles to travel around Russia, and it seems
possible that redbay ambrosia beetles could spread that way too.
Human transportation seems to have carried the beetle and its fungus
to the Gulf coast of Mississippi in 2009, the Florida Panhandle in
2010, central Alabama in 2011, northern Louisiana in 2014, and East
Texas in 2015. There is some evidence that the redbay ambrosia
beetle spread from Georgia and northern Florida separately, or got to
Georgia in 2001, not 2002. The beetle and laurel wilt are now found
in southeastern North Carolina, much of South Carolina, coastal
Georgia, almost every county in Florida, coastal Alabama and
Mississippi, along the Louisiana/Arkansas border (it was discovered
in sassafras in Arkansas last February), and in extreme East Texas.
Until 2009 the
beetle had only gotten as far north as the area around Charleston,
SC, but then it jumped to the Myrtle Beach area (Horry County)
bordering NC, and in March 2011 it was suddenly found near Colly, at
the eastern end of Bladen County, NC and when the NCFS looked for it,
it was found in three other counties within 15 miles of the first
site. Laurel wilt was found in Brunswick County in 2012, New Hanover
County in 2013, and now effects nine counties in NC. I wonder if
laurel wilt could have spread more than the NC Forest Service
realizes. One piece of good news is that a 2008 study predicted that
by 2015 laurel wilt would have spread across most of NC, except for
some of the northern Piedmont and mountains, but so far it is only
found in Bladen, Brunswick, Columbus, Duplin, New Hanover, Onslow,
Pender, Robeson, and Sampson counties, though it is still spreading
within those counties and human transportation has greatly advanced
the 'schedule' in other states. At the time sassafras was a wild
card and studies have now shown that the beetle tolerates cold well
enough to spread throughout the eastern US.
Symptoms of laurel
wilt vary by the species affected. Evergreen redbays turn wilted and
brown until the entire canopy is just dead leaves. There could be
signs of boring, such as sawdust and dried sap. Peeling the bark
back reveals dark lines in the sapwood beneath. Stricken trees
attract additional redbay ambrosia beetles and other beetle species.
The black twig borer is another Asian ambrosia beetle that attacks
redbays and other trees, but it only kills isolated branches.
Deciduous sassafras turn brown or display their bright fall color
early and lose their leaves. The fungus seems to spread through
interconnected roots in sassafras and avocado groves, and may be able
to do so in pondberry as well.
Individual trees
can be protected with fungicide for one to one and a half years at a
time and insecticides and beetle-killing fungi can reduce the beetle
population, but there is no way to protect an entire forest. So far
there don't seem to be any parasites available in Asia to naturally
control redbay ambrosia beetles, in contrast to emerald ash borer.
In 2006 all infested trees on public and private lands on Jekyll
Island, Georgia were removed in an attempt to get rid of the beetle,
but the beetle remained in 2007. Transporting untreated wood and
live plants long distances is very risky, but live plants and wood
from trees in the laurel family especially should not be transported
out of or through infested areas. Amazingly, while NC had county
quarantines and now a state quarantine against emerald ash borer,
there does not seem to be a quarantine against laurel wilt (see
www.dontmovefirewood.org/the-problem/state-state-information/north-carolina.html
) and some infested states lack regulations. Maybe the rationale is
that redbay wood is not often cut and transported.
The beetles and
fungus can live in a dead tree for more than a year, and, ideally,
infested wood should be chipped, burned, or buried on site. Leaving
infested wood exposed in a dump allows redbay ambrosia beetles to
reproduce and the fungus could be picked up by other beetle species.
In a study, no beetles or fungus were found 2 days after chipping,
but the wood still should not be considered clean. Covering a pile
of chips with plastic kills the beetles, but the chips could attract
new beetles and should not be transported. Advice to Florida avocado
growers claims that high-speed mechanical pruning equipment does not
spread laurel wilt, but hand saws can. Wounds such as pruned
branches attract beetles. Cutting roots linking trees in infested
groves using trenchers, etc. might help protect trees such as
sassafras once an infection starts in a grove. Coppicing might allow
homeowners to keep trees alive, but at a smaller size.
Redbays if not
other trees can resprout from the ground after the tops are killed
and there are seeds in the soil, so they probably don't face
extinction, but this new growth can get re-infected as it gets
larger. Strangely, redbays often re-sprout from the roots, while
thicket-forming sassafras often re-sprout from the trunk. When
people talk of trees being killed by disease, it is usually unclear
if they mean the entire tree is dead or if the roots are still alive,
so that regeneration is possible. Also according to the Georgia
Forestry Commission, dead redbays rot faster than sassafras, but
sassafras wood is also supposed to be rot-resistant. Researchers are
testing resistant varieties and storing germplasm for future
restoration, though it may be hard to store redbay seeds longterm.
Fear of laurel
wilt or other new pests should not result in the killing of healthy
trees. The situation may be the same as with emerald ash borer,
where studies have shown that preemptively removing ash trees is more
expensive than waiting and does not stop the borer. I might have
seen this happen in Durham in December, and I am not advocating
pointlessly hastening the downfall of these trees.
Redbay Ecology
and Culture
Redbay and related
trees are important members of forests in the coastal plain and
barrier islands and are valuable for both wildlife and humans.
Redbay grows naturally in the coastal plain from southern Delaware to
East Texas and into southern Arkansas, as well as the Bahamas, so I
don't have a lot of personal experience with it here in the Piedmont.
It typically grows near water but also sometimes in drier sandy
soil, often under longleaf pines. The Bald Head Woods Reserve
conserves rare maritime forest on the coast of NC, where redbay is or
was an understory tree making up about 11.4% of the vegetative cover,
while in Florida's Everglades, redbays make up 30% of the canopy in
forested areas, and possibly more in certain habitats. The loss of
redbays could greatly change ecosystems, such as by opening gaps that
non-native plants will fill. Redbays can grow up to 70' tall and 3'
wide and are valued as ornamentals and were used to reclaim phosphate
mines. Swamp bay is similar, possibly just a subspecies of redbay,
and grows in swamps over about the same range. Silkbay is another
subspecies or a separate species, found in oak-pine scrub habitat in
Florida.
US
animals very threatened by the laurel wilt epidemic are Palamedes
swallowtails, large black butterflies with yellow markings whose
caterpillars eat mainly redbay, three tiny leafmining moths in the
Phyllocnistis genus,
and the redbay psyllid (Trioza magnoliae),
an insect that forms swollen galls on redbay leaves. Palamedes
swallowtails feed only on redbay and possibly sassafras; in
experiments their caterpillars can feed on exotic camphortrees, but
females don't know to lay eggs on these Asian trees. A study in
Mississippi found that the swallowtails were three times less common
where laurel wilt had been around for three years or longer.
Palamedes swallowtails are an important pollinator of the
yellow-fringed orchid (Platanthera ciliaris),
and possibly related orchids with deep flowers, though the orchid
also grows where these swallowtails are absent, including in the
Triangle and in western NC. Spicebush swallowtails are another
pollinator, and also depend on trees in the laurel family. Few other
animals seem to feed on redbay leaves, and they have alternatives.
Avocado weevils eat plants in the laurel family, and despite their
name, might prefer redbays. Deer and black bears eat the leaves and
fruit. The fruit is bitter, but is eaten by turkeys and many other
birds, while bobwhites and a seed beetle eat redbay seeds.
Fresh or dried
leaves can be used like bay leaves in cooking. Redbay is a potential
graft for avocados and a source of disease resistance through
crossbreeding. According to Plants for a Future (pfaf.org), redbay
had many uses in Seminole herbal medicine, such as treatment of
constipation, rheumatism, fever, and to induce abortion. Bays in
general are very important in Seminole and Miccosukee traditional
medicine and ceremonies in Florida. Its red wood polishes well and
is used in cabinetry and other interior uses and boats, but the wood
is strong but brittle and straight trees are rare.
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Sassafras leaves
taking on fiery colors in the fall ©
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Sassafras
Ecology and Culture
Sassafras is an
important but probably overlooked tree that grows throughout much of
the eastern US, from southern Maine and Michigan to East Texas and
the Florida Panhandle. It can grow 90' tall, 6' across, and live
1000 years (longer than oaks or UNC's ancient Davie Poplar, a huge
tuliptree), but around here they are usually 15' tall or shorter.
The best and most public specimen I can think of is a pretty grove of
saplings about 15' tall where Barbee Road crosses over I-40 in
Durham. Sassafras have very distinctive soft and aromatic
leaves, which can be oval, mitten-shaped, trident-shaped, and rarely
five-lobed, probably depending on the amount of shade. Sassafras
fills different niches across its large range, but around here they
often grow along fencerows and as understory trees in somewhat moist
and rich soil near streams and on hillsides. Sassafras is somewhat
common in the Triangle, but might escape notice because it is usually
small.
Many insects
feeding on sassafras, including colorful and well-known spicebush
swallowtails and Promethea, Cecropia, Io moths, and several less
well-known moths, sassafras borers (a long-horned beetle), and other
insects, but most or all of them have options if many sassafras
succumb to laurel wilt. Deer, rabbits, and groundhogs also browse on
sassafras. Black bears, fox squirrels, turkeys, bobwhites, robins,
towhees, mockingbirds, catbirds, pileated woodpeckers, bluebirds,
phoebes, and other birds eat the late summer or fall fruit.
Leaves
can be eaten fresh and gumbo filé
and soup thickener is made from dried and powdered shoots. Tea is
made by boiling the washed roots and adding sugar or using the
flowers. Twigs were boiled, mixed with molasses, and fermented for
beer. Various parts of sassafras were used against many illnesses,
and It had such a reputation that it was a principal export of
Jamestown and other English colonies. It is probably more useful for
its taste than as a cure, and has been used in soap, perfumes, and
flavoring. Sassafras' popularity came to an end when the FDA
classified its oil, safrole, as carcinogenic, though the risk might
be overstated. Safrole is used to make the drug ecstasy, but the oil
is usually harvested from related trees. Sassafras is also a source
of dye. Sassafras wood is fragrant and was used in beds and chicken
coops in an attempt to repel pests, as well as for posts, railroad
ties, barrels, buckets, furniture, finishing, boats, and dugout
canoes, as it resists rot and shrinkage.
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A grove of
miniature sassafras in January ©
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Laurel Wilt and
Imperialist Globalization
Laurel wilt is a
disaster that could have been prevented and is only one of several
invasive pests harming trees in the US in recent years, and
non-natives species that run wild are a major problem worldwide,
rarely highlighted by opponents of “free trade.” Changes in
global trade patterns have caused trends in the organisms that reach
the US and become established, despite the enactment of Federal
regulations since 1912. A 2010 study (Historical Accumulation of
Nonindigenous Forest Pests in the Continental United States,
posted online) found that about 2.5 established non-native forest
pests were detected per year from 1860 to 2006 (though studies of
aquatic and other habitats have found accelerating colonization
rates), but the most damaging pests (all 16 microbes and 62 insects,
14% of the insect total of 455 species) were discovered at a rate of
one about every 2 to 2.5 years. The rate varied by how the pests
live, so the highest rate of detection of leaf eating pests in the
USA was around the 30's, while sap-feeding insects peaked in the
early 1900s, but had a smaller secondary peak in the late 20th
century that the study left unexplained. Discovery of high-impact
pests and phloem vessel and woodboring insects has greatly increased
since the 80's. 56% of the new insects detected between 1980 and
2006 were in this borer category. 56% of the high-impact pests with
known detection dates came before 1930 and then fewer were detected
per year until the trend greatly reversed around 1990, so that 24% of
the total were detected after 1990. Since 1990 an average of 1.2
high-impact pests have been found per year, almost three times the
rate from 1860 to 1990. 44% of the insects found between 1999 and
2006 were in the high-impact category. The study suggests that the
rate has increased because of the use of wood in containerized
shipping and heightened vigilance. In Canada detections peaked in
the 40's-50's but only declined in the 80's, which a study attributed
to new laws across the border in the US and a 1976 Canadian
phytosanitary law, but I wonder if this could also relate to Canada's
changing relations with US and British imperialism, effecting who
Canada trades with and what laws are made.
Globalization seeks
to 'flatten' the world, and in a sense that could mean our forests
will be flattened, in exchange for greater business profits. Any
long-distance trade and travel gives exotic organisms a chance to
hitch a ride, but offshoring factories just to exploit workers and
resources in other countries and importing labor rather than paying
higher wages to attract workers who are already here increases the
chance that something disastrous will become established. American
species, from goldenrods to largemouth bass, likewise cause problems
when transported to new places. In the Eastern US there has already
been significant to catastrophic damage to American chestnuts, elms,
Fraser fir, hemlocks, ashes, American beech, flowering dogwoods,
butternut, black walnut, bays, sassafras, Western soapberry, and
other trees, and serious threats to oaks and pines are waiting in the
wings, in addition to damage caused by bad land management, the
extinction of native animals that were beneficial for plants,
competition with non-natives, air pollution, and climate change.
Harm to trees in turn affects other plants and animals and the human
inhabitants of this forested region.
National Invasive
Species Awareness Week is February 27-March 3 ( www.nisaw.org/
)!
Some links about
laurel wilt:
ncforestservice.gov/forest_health/forest_health_laurelwiltfaq.htm
terrain.org/articles/22/cerulean.htm
About ambrosia
beetles:
About sassafras:
About redbay:
About the
Palamedes swallowtail:
entnemdept.ifas.ufl.edu/creatures/bfly/palamedes_swallowtail.htm
General
non-native issues:
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