Fire Blight Goes Under Wraps
The bacterium that causes fire blight in apples and other fruits
doesnt linger in a trees older vascular system in numbers
sufficient to cause disease, scientists with USDAs Agricultural Research
To make this discovery, scientists at the agencys
Appalachian Fruit Research Laboratory in Kearneysville, W. Va., built two
aseptic, whole-tree arborspheresa kind of plastic growth
chamberover four severely blighted, 12-year-old Rome Beauty apple trees.
First, the scientists heavily pruned the trees in the fall to
remove any cankers or damaged bark that might house bacteria. Later, they
applied dormant insecticidal oil to kill any insect eggs, and used a copper
compound on two trees to eliminate any surface bacteria.
Then, in April, they created the arborspheres, each with an
untreated and a copper- treated tree. Made with clear plastic-and-pipe frames,
the structures were equipped with air supply systems and filters to block
outside bacteria from entering.
After three months in the arborspheres, no bacteria were detected
on petri dishes left in the structures for four days. Surrounding trees not
protected by a sterile atmosphere were heavily infected with fire blight.
Results from this research can help growers. Extremely heavy
pruning causes an overabundance of new, tender shoots that are more susceptible
to fire blight infection. Therefore, when trees are dormant, growers should
remove only the blighted shoots and large cankers. Proper pruning should also
ensure adequate light penetration into the tree canopy to maintain good tree
More details on this story appear in the June issue of
Agricultural Research, the monthly magazine of the Agricultural Research
Service. The story is available in HTML format on the World Wide Web at:
Scientific contact: Tom van der Zwet, USDA-ARS, Appalachian
Fruit Research Laboratory, Kearneysville, W.Va., phone 304-725-3551, fax