Plant Disease Notes - Bacterial Leaf Scorch Of Shade Trees
ANR-1050, New July 1997. This publication was prepared by Austin Hagan, Extension Plant
Pathologist, Professor, and Jacqueline Mullen, Extension Plant Pathologist
and Diagnostician, both in Plant Pathology at Auburn University.
Plant Disease Notes
Bacterial Leaf Scorch
Of Shade Trees |
Bacterial scorch, which is caused by the fastidious bacteria
Xylella fastidiosa, is known mainly as a disease of landscape and
fruit trees. Sycamore is the most common landscape tree host of this bacteria.
Other landscape tree hosts include mulberry, red maple, American elm, and
a number of oaks such as the pin, scarlet, southern red, laurel, water,
and shingle oak. Other diseases caused by X. fastidosa, all of which
are found in Alabama, are Pierce's disease of grape, plum leaf scald, and
phony disease of peach. Outbreaks of bacterial scorch in landscape and fruit
trees occur primarily in the southern half of the state.
Symptoms. Typically, scorch first appears in mid-summer as yellowing
and then browning of the edge of all the leaves on one shoot in one area
of the upper canopy of a tree. On sycamore leaves, the areas between the
larger veins turn brown but veins themselves remain green. Scorched sycamore
leaves often curl upward from the edge. On oak and sycamore, the leaves
stay on the tree until fall. The development of scorch symptoms on the leaves
is often intensified by drought. Over a period of several years, symptoms
gradually develop on other branches of a diseased tree. Growth of leaf scorch-damaged
trees slows and diseased limbs start to dieback. The decline of diseased
sycamore is particularly rapid.
Persistence And Transmission. Leaf scorch bacteria are transmitted
by grafting as well as by xylem-feeding leaf hoppers and spittle bugs. Root
grafts are another means of tree to tree spread. This bacteria resides in
the xylem or water-conducting tissues of the tree. In diseased trees, disruption
or slowing of water transport up to the foliage along with bacterial toxins
causes the scorching of the leaves, decline in vigor, and eventual tree
death.
Control. Control of the insect vectors of the scorch bacteria with
insecticides is ineffective in slowing disease spread. Bacterial leaf scorch
is best controlled by using the following strategies:
- Pruning scorched shoots shortly after symptoms are seen may stop further
spread of the bacteria.
- Injecting bactericides into the trunk of lightly damaged but valuable
specimen trees will suppress symptoms but will not eradicate the bacteria
in the xylem. Once the annual treatments are stopped, disease development
will continue.
- Fertilizing and irrigating may prolong the life of diseased trees.
Preferably, diseased trees should be removed to prevent further spread
of the bacteria.
- Avoid planting susceptible tree species, especially sycamore, in scorch-prone
areas.
For more information, call your county Extension office. Look
in your telephone directory under your county's name to find the number.
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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