Oleander Plant Diseases – How To Treat Diseases Of Oleander Plants


By: Victoria Blackstone

Oleander shrubs (Nerium oleander) are tough plants that typically need little care to reward you with a profusion of colorful flowers in summer. But there are some diseases of oleander plants that can compromise their health and hinder their ability to bloom.

Oleander Plant Diseases

Bacterial pathogens are the culprits behind the primary oleander plant diseases, although some fungal pathogens may also infect oleanders. These organisms can infect plants through pruning cuts, and they’re often transmitted by insects that feed on the plant tissue.

Some diseases of oleander plants may look like other oleander problems, such as cultural disorders that include insufficient water or nutrient deficiencies. Troubleshooting tip: Take a plant sample to your local Extension office for their expert diagnosis of specific oleander problems.

Oleander leaf scorch

Oleander leaf scorch is caused by the bacterial pathogen Xylella fastidiosa. Symptoms include drooping and yellowing leaves, which are also symptoms of drought stress or nutrient deficiencies. However, if an oleander is drought-stressed, the leaves begin turning yellow at the middle and then spread outward.

Leaf scorch disease causes leaves to begin turning yellow from the outside edges toward the middle. Another way you can identify leaf scorch from drought stress is that wilted oleander plants suffering from leaf scorch do not recover after you water them.

Oleander knot

Oleander knot is caused by the bacterial pathogen Pseudomonas savastonoi pv. nerii. Symptoms include the appearance of knotty growths, called galls, along the stems, bark, and leaves.

Witches’ broom

Witches’ broom is caused by the fungal pathogen Sphaeropsis tumefaciens. Symptoms include a closely massed group of new stems that arise after shoot tips die back. The new stems grow only a few inches (5 cm.) before they also die.

Treating Oleander Diseases

While there are no cures for these bacterial and fungal problems, there are steps you can take to help prevent or control oleander plant diseases.

  • Cultivate healthy plants by planting them in full sun, watering them in times of drought and fertilizing them according to soil-test recommendations.
  • Avoid using overhead irrigation, such as sprinklers, because this keeps the plants wet and fosters a breeding ground for disease organisms.
  • Prune your plants to remove dead and diseased stems and twigs, and disinfect your pruning tools between each cut in a solution of 1 part bleach to 10 parts water.

Caution: All parts of oleander are toxic, so use caution when using any oleander disease treatment. Wear gloves if you handle the plants, and don’t burn diseased limbs, because the fumes are also toxic.

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How To Treat White Spots On An Oleander Plant

The best treatment for scale on the oleander plant is to spray the entire plant with horticultural oil (source). The best time to spray is in the early spring when the new plant growth appears.

Buy a horticultural oil (link to Amazon) and use it as follows:

  • Mix two – five tablespoons (1.25 – 3.1 ounces) of horticultural oil with 1 gallon (4.5 liters) of water.
  • Pour the solution into a spray bottle.
  • Spray the top and underside of all leaves and stems on the plant down to the soil lie.
  • Repeat the process in five to six weeks and once more in another five to six weeks.
  • Always take precautions when mixing any garden sprays. Wear protective clothing, eyewear, and gloves.
  • If the infestation is too big, you may have to prune the plant by snipping off the affected leaves and stems or by destroying the plant completely.


Common Pests

Here's a list of commons pests for perennials and what you can do to get rid of them.

Caspid Bugs

Caspid bugs are highly mobile and are known for extracting sap from buds and young shoots and producing toxins. As the plant grows, the toxins cause jagged tears and irregular shaped holes.

Although the bugs will likely move on to another plant by the time you notice the damage, they tend to visit the same plants year after year. Treat susceptible plants with an appropriate insecticide.

Cutworms

Cutworms sometimes attack plants at or below the soil level but are not likely to feed from established plants. They are most active in the early gardening season.

Control cutworms by hand-picking them at nighttime with a flashlight and gloves. Toss cutworms into soapy water, and recheck the plant for more cutworms over the next few nights.

Leaf Miners

If you notice leaves with “tunnels” between the tissue layers of the leaf, your plant is likely infected with leaf miners. These tunnels show the path that the little larvae have made while eating up your plant. Since there is no sufficient insecticide, you’ll need to destroy any affected leaves to help reduce the miner population.

Slugs and Snails

Slugs and snails can quickly destroy new growth and leave foliage holey. They particularly enjoy feeding on delphiniums, dianthus, and hostas to name a few. Encourage frogs and toads to make homes in your garden, as they naturally will take care of slugs and snails.

Swift Moth Caterpillars

Swift moth caterpillars damage the roots of plants and rarely feed above ground. Gardeners tend to find the caterpillars when pulling plant out of the soil for division.

Deter swift moth from laying eggs around the plant by keeping the soil around the plant free from weeds.

Vine Weevils

Young vine weevils often sever the shoots of plants, separating the crown from the root, whereas adult vine weevils tend to attack leaves.

Remove weevils by hand and place them into a bucket of soapy water. Apply a nematode to plants heavily infested with vine weevils.

Yuck! This plant is infested with snails.


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Watch the video: Gardening Tips: How to Grow Oleander


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