Bacterial
Leaf Scorch
is caused by the bacterium, Xyella Fastidiosa,
which colonizes and clogs the tree’s water conducting
tissue (xylem). This disrupts water transport in
roots, branches, and leaves due to the large amounts of
multiplying bacteria and their by-products. The presence
of the bacterium in the vascular tissue can only be
identified through microscopic or laboratory tests.
Symptoms and
Diagnosis
Xyella
fastidosa
is
transmitted to healthy trees by leafhoppers and
spittlebugs and possibly other feeding xylem insects or
birds. Bacterial Leaf Scorch affects red oak, elm,
sycamore, mulberry, maple and sweetgum. Diagnosis can be
based on time of symptom development, leaf color change,
and the annual progression of the of the disease
throughout the tree. Symptoms appear in mid to late
summer and on into early fall. Leaf scorch describes the
death of tissue along the edge of the leaf. Sometimes
called marginal leaf burn, this symptom develops when
water needed by the plant cell at the edge of the leaf
does not reach those cells in adequate amounts to
replace what is lost during transpiration and growth.
This occurs in drought conditions, high summer
temperatures, soil compaction, root loss, and the fungi
or bacteria which invade and plug or destroy the xylem (water
conducting vessels) in the plant. This intermediate
transition zone appears dull, pale green in color, and
has a "water soaked" appearance. Finally the entire leaf
dies and turns brown. Symptom development is also
hastened during periods of above normal temperatures.
Control
There is no known cure for Bacterial Leaf Scorch and too
little information is available on the disease
development and spread to recommend an effective control
measure. Injecting, disease trees with antibiotics
reduces symptom development but cannot eliminate the
pathogen, and injections are expensive and must be
repeated. In all honestly be prepared to lose the tree
in a few years. Tree
life, however, may be extended by improving general tree
vigor with irrigation, soil amendments and pruning
should also be monitored. Branches can be
therapeutically pruned well below the leaves, possibly
preventing or minimizing the spread of the pathogen in
the tree. Remember always sterilize your pruning
equipment.
