Posted: February 1, 2011
Des Moines, Iowa - The most economically valuable tree in Iowa
is under a possible threat from a beetle that is about the size of
the period at the end of this sentence.
Thousand cankers disease (TCD) has been killing
black walnut trees
in the Western U.S. since the 1990s. It is not currently in Iowa, but
is as close as Rocky Ford, Colo., to the west and Knoxville, Tenn.,
to the south.
"The introduction of TCD into Iowa would have disastrous effects
economically and environmentally to the wood industry in the state,"
said Tivon Feeley, with the forest health program at the Iowa
Department of Natural Resources.
Iowa's estimated 979 million board feet of sawlog-sized black
walnut standing in the woodlands is the third largest state volume in
the nation and valued at nearly $1.5 billion. The economic loss in
Iowa to woodland owners and associated businesses that annually
harvest more than 9.3 million board feet would be an estimated $62
million per year.
"Some experts believe that TCD has the potential to decimate black
walnut in the same way Dutch elm disease, emerald ash borer and
chestnut blight have destroyed their respective hosts," Feeley said.
The disease is caused by a walnut twig beetle that carries a
fungus which is spread as it tunnels through tree tissue. Beetles can
reach high populations and numerous cankers can develop. Instead of
one large girdling canker, tree decline and death appears to result
from the high number of cankers.
"We placed two logs about eight inches in diameter and two feet
long in a box and eventually recovered around 23,000 beetles," said
Ned Tisserat, professor with Department of Bioagricultural Sciences
and Pest Management at Colorado State University.
Rapid detection and removal of infected trees is currently the
primary means of managing thousand cankers disease. Stopping or
slowing its spread from infested areas relies on quarantines of wood
products and on public education.
In addition to Colorado and Knoxville, Tenn., the beetle has been
killing black walnuts in New Mexico, Arizona, Utah, Idaho, California
and New Mexico.
"It comes back to do not move wood," Feeley said. "The reason TCD
is in Knoxville is because it was brought there in wood from a
contaminated area from the west. Don't move firewood, wood logs or
other untreated wood products."
Very little is known by the public about thousand cankers disease
of black walnut, Feeley said.
"Scientists are investigating how serious of a threat this disease
will be in the eastern U.S., and until more facts are learned,
woodland owners are encouraged not to harvest their trees, but to
continue working with their local forester to keep their woodland
healthy," he said.
A more intensive survey of declining black walnut trees has been
proposed in a grant to the U.S. Forest Service.
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