Oleanders under attack in Fallbrook area

Drought-tolerant oleander shrubs have long been a good choice for gardeners in Southern California. The evergreens grow well in Mediterranean climates, besides being native to the Middle East, India and Southwest Asia. They like sunny spots and light shade, growing best in well-drained soil and tolerating dry environments.

Used often to create living fences, full-grown oleanders can measure six- to 12-feet tall and wide. The fragrant scent of their white or pink flowers fill yards from summer to fall making them an attractive part of any garden. Like many plants, though, every part of the oleander is poisonous if ingested. Also, its sap may irritate some people’s skin so gloves are advised for anyone taking care of or removing them.

While oleanders have many good features, the ones in California are now being attacked by a disease spread by the glassy winged sharpshooter, an insect almost one-half inch long. Called oleander leaf scorch, the disease is a bacteria that grows in the water-conducting part of the plant, the xylem tubes. When the bacteria grow, they block the tubes which prevents the shrub from getting water and nutrients.

According to a report to the legislature in 2012 from the California Department of Food and Agriculture, “The glassy-winged sharpshooter was first reported in California in 1994 but probably arrived and established itself in the state in the late 1980s. It is native to the southeastern United States and northeastern Mexico. It feeds on the xylem fluid of a large number of plants. The sharpshooter builds up large populations on a diverse array of host plants and is an aggressive flyer, traveling greater distances than native sharpshooters.”

The report also included the glassy-winged sharpshooter infestation of the vineyards in the Temecula Valley, spreading Pierce’s disease (xylella fastidiosa) in the late 90s. Over 300 acres of grapevines were destroyed in August 1999.

The experts said that several strains of this bacterium exist, attacking and causing damage to different host plants including grapes, citrus, stone fruits, almonds, oleander, and certain shade trees such as oaks, elms, maples, and sycamores. It also affects mulberry, olive and liquidambar trees.

As with the other plants, the glassy winged sharpshooter feeds on the xylem sap in the stems, picking up the X. fastidiosa bacteria in the process, acquiring the infection itself, and therefore infecting any plant it feeds on after that.

While drought-stressed leaves of oleanders turn yellow on all their branches and usually from the middle outward, leaves of infected oleanders turn yellow from the edges, or tip, inward on a few branches at a time and do not recover with watering.

The progression of oleander leaf scorch is faster in hot and dry weather. There is no cure for the disease; dying branches can be cut off but the bacteria spreads so quickly that the rest of the shrub is already affected before more leaves start turning yellow. The shrubs die within three to five years after being infected.

Removing an entire shrub that shows signs of the bacteria may or may not protect nearby shrubs but is the best option as the plant will die. Because the oleander leaf scorch bacteria cannot live in soil, it is safe to replace the sick oleanders with other kinds of plants.

There are many other drought-resistant shrubs that can be planted in place of dying oleanders including succulents and native California plants. Local nurseries can provide suggestions and advice.

For more information on oleander leaf scorch or the glassy-winged sharpshooter, visit http://www.cdfa.gov.