Oleanders are warm-climate shrubs that perform best under a hot sun. The multiple trunks of oleanders can reach a height of 12 ft., with some varieties growing to 20 ft. tall. As they stretch up, these plants also develop as mounds of dark-green thick foliage and flowers that bloom summer through fall. Although oleander requires simple care -- it grows in any soil type, tolerates shade and resists droughts -- it also succumbs to certain diseases and can pose problems for you.
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Oleander Leaf Scorch
Despite this disease’s name, the sun doesn’t cause oleander leaf scorch. This is a bacterial infection started by Xylella fastidiosa, a bacterium that hitches a ride with insects to reach the shrubs. Oleander leaf scorch isn’t a seasonal problem, and the signs of this incurable and fatal disease can appear any time. First you'll notice a yellowing at the foliage’s outer edges. This expands towards the center as the disease evolves. Eventually the leaves die. It can take three to five years for the entire shrub to succumb to oleander leaf scorch.
Like every living thing, oleanders are part of the food chain. These shrubs are the only food source of the oleander caterpillar. This 2-inch-long orange creature with clumps of black hair throughout its body is only a pest to be controlled if you can’t tolerate it. Although oleander caterpillars can quickly work their way through your shrub’s foliage as it feeds before metamorphosis, it doesn’t kill your plant. New foliage grows back and becomes dinner for the next generation of caterpillars. Stink bugs, wasps, tachinid flies and red imported fire ants are natural enemies of the caterpillar and are present in pesticide-free gardens. Removing the moth larvae by pruning the leaves they’re on is another method of preventing caterpillar damage.
Botryosphaeria dieback is a fungal infection that kills oleander branches and shoots. This fungus usually infiltrates the defenses of a plant that is already weakened from other conditions. In oleander’s case, the stress of an extended drought or freeze damage can leave the shrub susceptible to a Botryosphaeria dieback attack. Remove all the infected plant parts, which will appear discolored when compared to healthy wood, to prevent the spread of the disease.
Oleander’s attractiveness comes with a dangerous side, posing a possible problem. According to Clemson Cooperative Extension, this beautiful and adaptable landscape plant is extremely poisonous and can be fatal if ingested. Skin contact and inhaling fumes if the plant is burned also cause health problems. Therefore, oleander isn’t a plant to have around young children and pets -- or unaware adults.