What Are the Causes of Dying Oleander?

Oleander Leaf Scorch

• An epidemic among oleanders, leaf scorch is killing the shrubs by the thousands. The San Diego Master Gardener Association estimated in 2011 that more than 90 percent might die off within the next few years. Leaf scorch is caused by a new strain of the Xylella fastidiosa bacteria, which is spread by the glassy-winged sharpshooter insect, a brown bug with clear wings that has spread from the southeast United States. Leaf scorch is incurable, and will kill the oleander within three to five years. Symptoms are leaves that droop, turn brown then die.

Caterpillars

• The polka-dot wasp moth is a beautiful, colorful insect with a bright red and blue body, and iridescent bluish-black wings with white dots. Its larvae, the oleander caterpillar, is bright orange with clumps of black hairs all over the body. These caterpillars feed voraciously on oleander shrubs, and can defoliate the entire bush if they're present in large quantities. Caterpillars can be removed by hand, or if they're too abundant for easy removal, the oleander can be treated with the insecticide Bacillus thuringiensis, usually sold in nurseries as Bt.

Witches'-Broom Disease

• Caused by a fungus, Sphaeropsis tumefaciens, "Witches' broom disease" infects oleanders, causing swelling and galls on the older branches and trunks of the shrub. The common name comes from the way infected branches will produce a tangled, broom-like clump of small shoots. The disease spreads easily in hot, humid weather and has no treatment. Plants infected with the fungus first show yellowing, dying leaves, then swollen growths on the branches, followed by the branches -- and eventually the entire shrub -- dying.

Sooty Canker

• Another fungal disease, sooty canker, is caused by Hendersonula toruloidea. The fungus infects the oleander through cracks in the bark or areas stressed by freezing, pruning or excessive sun exposure. Once infected, the branches wilt, develop cracks and holes, and eventually the bark peels away to expose black masses of fungus. Sooty canker can be prevented by keeping oleanders healthy, and by removing any infected limbs. Pruning must be severe in a badly infected bush, and should be done in the fall or early spring.