Oleander (Nerium oleander) is a flowering shrub native to Africa, Southeast Asia and the eastern Mediterranean. It is hardy in U.S. Department of Agriculture plant hardiness zones 8 through 10. Growers appreciate its durability, rapid growth rate and colorful flowers. Its blossoms in red, pink, yellow, white and salmon contrast with its large, leathery, green leaves. At maturity, oleander stands as tall as 20 feet, but gardeners can prune it carefully to grow it as a small flowering tree. Although oleander is low-maintenance and hardy, it is susceptible to several diseases and pests.
The oleander plant is toxic to humans and animals when ingested. Touching the plant can cause skin irritation. Avoid burning oleander leaves or branches. Do not plant it in areas commonly used by young children or animals.
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Oleander Leaf Scorch
Oleander leaf scorch, a bacterial disease, is found on oleander plants growing in the southern United States. Sharpshooters, which are leafhopper insects, spread the bacteria Xylella fastidiosa with their mouth parts as they feed on leaves.
Symptoms of oleander leaf scorch include stems drooping and leaves turning yellow. The edges of the leaves turn dark brown before eventually dying.
No cure or treatment for oleander leaf scorch exists. Pruning damaged branches and leaves is useless because the bacteria spread quickly through the plant’s vascular system.
The best defense against oleander leaf scorch infection is using a systemic insecticide containing the chemical imidacloprid. The product should be labeled as safe for flowering shrubs.
Oleander aphids have bright-yellow bodies with black appendages. Adult females may or may not have wings. Nymphs are smaller versions of the yellow and black adults. Oleander aphids range from 6/100 to 1/10 inch long.
They ingest sap from tender shoots of new growth. The damage is primarily aesthetic -- swarms of the aphids covering stems and leaves. After an ongoing heavy infestation, an oleander is at risk of stunted growth or deformity.
Cultural changes help fight oleander aphids. Less frequent pruning, fertilizing and watering discourages new growth, minimizing the oleander aphid population. Additionally, horticultural oil kills aphids by saturating their bodies.
The oleander caterpillar is bright orange with black spots and small sections of black hair. The caterpillar feeds on oleander exclusively, apparently unharmed by the plant’s toxicity. Upon emerging from yellow-green eggs on the underside of oleander leaves, oleander caterpillars quickly devour entire leaves and flower clusters.
Each caterpillar builds a silk and hair cocoon on a branch near the plant's stem or on the stem at the soil line. An adult moth -- the polka-dot moth -- with a bluish-black body and white spotted wings leaves the cocoon; within nine days from that point, it mates, lays eggs and dies. Multiple generations of moths and caterpillars are born during the summer feeding season.
Insecticide containing the chemical permethrin is effective in controlling the oleander caterpillar.
False Oleander Scale
False oleander scale is a hard-shelled, sucking insect that affixes itself to a leaf and removes plant sap. The scales cluster, appearing as small, white specks or spots on the surface of leaves growing on the upper part of an oleander plant. Individual scales are tiny; a male is about 3/100 inch long. The females deposit eggs under their hard shells. The nymphs crawl out of the eggs and find permanent locations on leaves before inserting their mosquitolike mouth parts to draw sap. The nymphs mature and lay eggs within five weeks. A heavy infestation causes the plant to lose most of its leaves.
The best defense against false oleander scale is horticultural oil. The insects die in place but do not fall off. Gardeners must scrape the dead shells or scales off the leaves.
To get ahead of false oleander scale or oleander aphid infestations, begin spraying your oleander with horticultural oil in early spring when its new growth appears. Purchase a horticultural oil labeled for flowering shrubs. Mix 2 to 5 tablespoons of horticultural oil with 1 gallon of water. Carefully pour the solution into a handheld sprayer. On a windless day, spray the top and underside of all oleander leaves and stems down to the soil line with the solution. Repeat the application in five to six weeks. Then repeat it once more in another five to six weeks. Use caution when mixing and spraying the oil. Wear clothing that covers your skin, including gloves and protective eye-wear.
Insecticide with Permethrin
To combat an attack from the oleander caterpillar, spray your oleander in early spring, before it flowers, with an insecticide containing permethrin. Mix 1/2 to 1 teaspoon of insecticide with 2 gallons of water. Pour the mixture into a handheld sprayer, and use it to spray the entire plant, including the top and underside of leaves and all branches and stems.
Permethrin is highly toxic to humans and pets when wet. Keep people and pets away from the treated area while spraying and afterward until the solution is dry. Cover all your skin by wearing a long-sleeved shirt, long pants, socks and shoes. Use chemical-resistant gloves and protective eye-wear, too. Avoid breathing the spray, and do not apply it under windy or rainy conditions. Wash with soap and water after the application, and launder your clothes before wearing them again.
Permethrin kills fish and aquatic invertebrates. So do not apply it within 25 feet of ponds, rivers, streams, lakes, marshes or reservoirs.
Do not reapply the insecticide solution unless a new infestation is present. One application can eliminate oleander caterpillars for one or more years.
Insecticide with Imidacloprid
Eliminate oleander leaf scorch caused by sharpshooter insects by applying a flowering shrub insecticide containing imidacloprid. Make the initial application at the first sight of the insects, but do not apply it when the shrub is flowering because imidacloprid is highly toxic to bees.
Mix 1 1/2 teaspoons of the insecticide with 1 gallon of water, and put the solution in a handheld sprayer. Use it to saturate all leaves, branches and stems of the oleander; ensure you coat the tops and undersides of leaves. Reapply the solution at 10- to 14-day intervals if the sharpshooter insect infestation remains.
Imidacloprid is toxic to aquatic invertebrates. So do not apply within 25 feet of ponds, rivers, streams, lakes, marshes or reservoirs. Wear protective clothing, such as a long-sleeved shirt, long pants, socks, shoes, gloves and safety glasses. Wash with soap and water after the application, and remove and launder your clothing. Avoid breathing the spray, and do not use the product under windy or rainy conditions.