A bacterium commonly identified with grape vines (Xylella fastidiosa)
is the suspected cause of “oleander leaf scorch,” which is resulting in the
slow deaths of thousands of oleanders in San Diego County. Likely
vectored by the glassy-winged
sharpshooter (Homalodisca vitripennis), a recent San Diego invader, the disease is fatal with no
Oleander leaf scorch was first identified in Palm Springs around 1992
and then moved into Riverside, L.A., and Orange Counties. The first signs
of infection are seen as an off-color shading and wilting of leaves,
which eventually turn brown. It appears as if the plant needs
water, but unfortunately this will not help. It may take some time for the entire plant to show signs of infection,
but within one to two years the plant will be dead. Cutting of infected limbs
may slow or prevent spread to the rest of the plant, but complete infection is unavoidable.
Oleanders are found extensively in the median of freeways and backyards of California, and this will likely result in massive losses and eventual
replacement at great cost. Oleanders are a hardy, dense shrub that can
grow to heights of 25 feet and require little water or maintenance.
Caltrans has planted approximately 25 million in Southern California.
Of particular concern is the spreading of Xylella fastidiosa to other species, such as almonds, alfalfa, plums, and olive trees.