Description: Bacterial leaf scorch (BLS) is a chronic, eventually fatal disease that is most noticeable in theearly fall. Urban trees such as sycamore, red maple, dogwood, American elm, and several species of oak (red, pin, scarlet, southern red, laurel, turkey, shingle and water) can become affected and eventually die. Scorch appears as an irregular scalloped browning along the leaf margin bordered by a yellow halo. Leaf discoloration begins at the leaf margin and moves toward the midrib. Symptoms reoccur each year and spread over the tree’s crown, thus reduction in growth and dieback are common in affected trees.
Symptoms: BLS colonizes and physically “clogs” the tree’s water conducting tissues or xylem. Water transport becomes disrupted in roots, branches, and leaves due to large amounts of multiplying bacteria and their by-products. The presence of the bacteria also triggers a reaction in the tree that plugs the xylem, further impeding water transport and eventually killing the tree.
It is still somewhat a mystery as to how this infection is contracted and spread. One agent that is known to spread this disease from a diseased to healthy tree is by xylem-feeding insects such as leafhoppers and treehoppers.
Action: One study, conducted by the University of Maryland, demonstrated a possible connection between BLS and water stress. It may be possible to prolong the life of BLS infected trees by applying supplemental water during the hot, dry parts of the growing season.
Replacing trees that are non-susceptible to BLS with those that are affected is the only real remedy right now. By identifying BLS early and helping stressed trees live longer, there is time to plant replacements and have them get established before you have to remove the BLS infected ones.
Certain antibiotic treatments, coupled with soil therapy have been shown to suppress the disease.
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