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Disease Management

Historically, management of the many diseases caused by X. fastidiosa has encompassed various strategies such as reducing host stress, planting hosts not known to harbor the bacterium, and removing infected hosts, vectors, and alternative hosts. In shade trees, it is not known whether therapeutic pruning (removing infected branches as they become symptomatic) or removing infected trees stops the spread of the disease, both within a tree or within populations of trees. Indeed, the random incidence of BLS within a tree planting leads one to suspect that X. fastidiosa also does not spread through root grafts, but this method of transmission has yet to be investigated. Management of BLS is made further difficult because it is not known how long hosts may remain asymptomatic prior to the first expression of symptoms.

The use of the antibiotic oxytetracycline to control X. fastidiosa has been attempted on hosts such as grape, plum, and shade trees. Such trunk or root flare injections, however, provide only seasonal relief from symptoms, do not work well in trees with advanced disease, and must be repeated annually to be effective. Further studies are needed to determine if such antibiotic injections are effective or phytotoxic long-term or if repeated wounding during the injection process has a negative impact on the tree.

Management of the diseases caused by X. fastidiosa through vector eradication has been attempted, but even with Pierce’s disease, where disease vectors are known, results are inconclusive. Trials evaluating the systemic insecticide imidacloprid are underway in infected shade trees. This compound is applied in a non-invasive manner to trees (as a soil injection) and is retained in the canopy for a 3-yr period. Ultimately, vector eradication may be useful only to prevent or reduce the rate of spread to adjacent plantings. More novel approaches to management of X. fastidiosa in grapes, such as biological control or biofilm disruption, are currently under study, but use of such techniques for BLS of shade trees may not be feasible for years to come.

In summary, there are few cost-effective methods for the management of BLS in landscape plantings. Current management recommendations include:

Maintain plant vigor. The best management tool for this disease is to maintain tree vigor. The development of oak leaf scorch is enhanced by other diseases, insects, and environmental stresses such as drought. Bacterial leaf scorch may also predispose infected plants to other disease and insect problems.

Practice sanitation. Branches that have died due to oak leaf scorch should be routinely removed. Infected trees that are in a severe state of decline should also be removed.

Use tolerant plants. In areas where BLS occurs, avoid planting highly susceptible trees, and design new tree plantings with a diverse complement of tree species. Management of BLS in many regions of the eastern United States may ultimately depend on the identification of germplasm tolerant to the disease.

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