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Tuesday, December 1, 2015

Correcting Oleanders with Leaves Browning Along the Edges

Q. We have one oleander approximately 2 years old and 4 new ones we purchased several weeks ago.  The older one (1st photo) and one of the new ones (2nd photo) have some leaves that are browning along the edges while the centers are still green; a few have tips that are browning too.  From what I've read, could the plants have leaf scorch or, "salt or boron toxicity"?

Two pictures sent in regarding oleander leaf scorch

A. You are right, this browning along the margin of oleander leaves, or leaf scorch as it is sometimes called, could result from a number of things.

One possibility is a bacterial disease that has been called Oleander Leaf Scorch. It is a bacterial disease which is rarer in plants than fungal diseases. This disease is carried from plant to plant by what we call "vectors". These vectors can be insects that feed on the "juices" of this plant or they can be transmitted by humans on pruning shears. This is why I am constantly reminding people to clean and disinfect their pruning equipment before they begin pruning and between plants if the plant they finished pruning appears to be "sick".

More information about oleander leaf scorch from the University of California

Leaf scorch can also because to buy a lack of water and excessive salts in the soil which can be made worse if plants do not get enough water. One particular salt that you have identified as a problem in our soils is boron. The other particularly troublesome salts contain sodium and chlorides. Salts that contain for plants, such as nitrogen, phosphorus, potassium and others can also cause leaf scorch if they are in excess. Fertilizer salts containing high levels of nitrogen can be particularly troublesome and cause plant damage if applied in excess, too close to the plant or when soils are dry.

What to do? Apply compost around the base of the plant and either wash it into the soil or lightly dig it into the upper surface of the soil.

Add more water. If you feel as if the plant is not receiving enough water, add more drip emitters. This is preferable to just increasing the number of minutes since everything watered by that valve will be affected. If you're fertilizing the plants, make sure the fertilizer salts that you apply are kept at least 12 inches from the trunk and applied near the emitters or bubbler. Make sure the soil does not become dry between irrigations because dry soils increase the concentration of salts already in the soil.

Lastly, cut the oleanders to the ground and let them re-grow from the base. If you apply more water, improve the soil and are careful with fertilizers and the plants still have leaf scorch during the next growing season, then dispose of them and to get new ones. Oleander leaf scorch will not be in the soil. It can only be transmitted from unhealthy plants to healthy plants either by insects or humans who are not careful about pruning.

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