OLEANDER LEAF SCORCH (OLS)
Major symptoms: Marginal scalloped chlorosis (yellowing), followed by marginal or tip leaf scorch, then die-back of twigs and branches. The disease seems to kill oleander within about two years of the first appearance of symptoms.
Distribution: Present in southern California, Arizona, Texas. Occurrence in other southern states is likely but not yet confirmed.
Oleander leaf scorch (OLS) is a lethal disease of oleanders (Neerium oleander L.) that was first noticed in southern California in the early 1990s. OLS continues to spread to new geographical areas. The strains of the bacterium Xylella fastidiosa that cause OLS (Purcell et al 1999) are distinctive from strains that cause disease in grape, almond, oak, peach or plum. On the basis of DNA analyses, the oleander strain appears to be a recent arrival to California. The oleander strain of Xylella fastidiosa may represent a new pathotype that can cause disease in other crops and ornamentals. However, inoculations of grape and peach with OLS strains of Xylella fastidiosa failed to cause infections that were detectable several weeks or months later. OLS strains infected periwinkles (Vinca major and Catharanthus rosea) and caused leaf scorching in both periwinkle species in the greenhouse.
The glassy-winged sharpshooter (GWSS, Homalodisca coagulata ) is closely associated with the spread of OLS along the coast of southern California but not in the Palm Springs area, where OLS can be severe. GWSS is native to the southeastern states (Florida through Texas) and has only been detected in California during the past few years but is now known to have occured in California since at least 1990. It is now as far north as Ventura on the coast and Bakersfield in Central California, where it is abundant on citrus but where OLS has not yet been reported. Isolated finds of GWSS have been recorded as far north as Lodi, but without evidence yet of permanent breeding populations. Besides its association with oleander leaf scorch, the glassy-winged sharpshooter is a principal vector of phony peach disease and Pierce's disease of grapevines, which are caused by different strains of Xylella fastidiosa.
Eradication of OLS or the glassy-winged sharpshooter is not feasible. Presently, the only measures to control OLS are to destroy oleanders that have definite symptoms. If the OLS strain does not have a wide range of plant hosts, rigorous practices of this sanitary measure may slow spread of OLS to other oleanders.
(AHP, January 2000)
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