What is Oleander Leaf Scorch?
A landscape icon in San Diego and throughout Southern California, the ubiquitous oleander (Nerium oleander) is falling victim to an incurable disease. Native to the Mediterranean region, these versatile shrubs with slender leaves and azalea-like flowers are a carefree screen, defining property lines, providing privacy or, as one gardener admitted, “separating me from the junkyard next door.” Oleanders may be shunned by some plant collectors as commonplace and by some homeowners for their toxicity – all parts of the plants are poisonous. But it’s difficult to dispute their utility as so many succumb, leaving unwanted gaps in area gardens.
Oleander Leaf Scorch is the reason the leaves on these long-lived shrubs are drooping, turning brown and dying. Individual branches die back; then, as more branches are affected, the entire plant dies. Oleander leaf scorch is a lethal disease of Oleanders that was first noticed in southern California in the early 1990s. Symptoms can be expressed year-round, although they may be more noticeable in late spring and summer; they develop more quickly in warm weather. As summer’s heat peaks and Santa Anas roar, the demise of infected oleanders will be accelerated. Some experts predict that more than 90 percent will die in the next few years. Leaves on one or more branches may yellow and begin to droop; soon the margins of the leaves turn a deeper yellow or brown, and the leaves eventually die. As the disease progresses, more branches of the plant are affected and the plant dies. Symptoms are much more severe and develop more rapidly in hot interior valleys than in cooler coastal areas.
There are two culprits. One is a new strain of the bacterium, Xylella fastidiosa, and the second is a relatively new insect vector, the glassy-winged sharpshooter, which spreads the disease from oleander to oleander. In each instance, the bacteria feed on the water-conducting tissue or xylem of the plant. As their numbers grow, the xylem is blocked, depriving the plant of water and nutrients. The disease takes its toll rapidly when the plants are stressed by heat and lack of rainfall.
The glassy-winged sharpshooter, a half-inch-long brown insect with clear wings, was brought into Southern California from the southeast United States. Biological controls limit its population and aggressive steps are being taken to prevent its spread into central and Northern California. Symptoms of oleander scorch were first spotted in the early 1990s in Palm Springs and Indio, in Riverside County, and Tustin in Orange County. In addition to San Diego County, Los Angeles, San Bernardino, Ventura and Santa Barbara counties have reported infected plants.
It can take three to five years from the time symptoms are spotted for an oleander to die. Cutting off affected branches may slow progress of the disease, but won’t stop it.
Luckily for San Diego, there are numerous, good options for replacing dead or dying oleanders that have been used as screens. Luckily, the bacteria that causes Oleander Leaf Scorch does not survive in the soil where the plant was growing. Thus other shrubs and trees can be planted in the same spot. In some cases, the oleanders’ demise can be an opportunity to bring new and unusual plants to the landscape that will serve the same purpose and are equally drought tolerant! As one should remove dead oleanders with caution because of their poisonious state, it is best to call a landscape professional to handle this as well as get ideas for new plant material from your local experts… Pacific Green Landscape, Inc.