Bacterial leaf scorch

Natural History
Red oak with BLS symptoms
Photo credit: Bugwood.org

Bacterial leaf scorch is caused by the bacterium, Xylella fastidiosa. This bacterium is limited to the xylem of infected hosts and is transmitted by xylem-feeding insects such as leafhoppers, sharpshooters and spittlebugs. The pathogen disrupts vascular function and, as a result, damage that is similar to drought damage begins to appear in mid-summer. Infected trees display leaves with scorching symptoms – including marginal necrosis and chlorosis. Leaves may eventually become completely brown and remain attached. Chronic infection can lead to stunting, dieback and witch's brooms. The host range is very wide, but the disease is most commonly observed in Florida on oaks (especially turkey oak), sycamore, sweetgum and elms. Control is not common on trees, but anti-biotic injections can be useful.


 

Identifying Characteristics

Identifying the injury: Foliage with marginal chlorosis, followed by necrosis. The necrosis is usually closer to the leaf margins. Leaves turn completely brown. Stunting, dieback and sometimes tree death.
Identifying the pathogen: X. fastidiosa is a microscopic rod-shaped bacterium that is not easily cultured on artificial media.
Susceptible trees: Wide host range including: oaks (especially laurel and turkey oak), sycamore, sweetgum and elms.

 

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