Oleander disease

[wysteriangnome]

We have several large Oleander bushes/trees on the property. This spring an arborist told me one of the large Oleanders in the front yard had an incurable disease & eventually it will die. So, early summer I cut all the stalks back from approx. 10 ft., down to 3 ft., doused it with buckets of water & a little dishsoap, as I had heard that works with some problems. Well, the new growth seems healthy so far. Now, I see a couple more large ones have some of the same discoloration of leaving dying away. I would hate to attempt the same drastic measures, but may have to? I don't even know if the one I cut back will continue to grow healthy. Any information or experience with the Oleander disease (I was not told the name of the disease) would be appreciated. Do you think I should continue with occasional soap/water dousing? Thank you

[rainbowgardener]

I don't know much about oleander, since it doesn't grow where I am, but I looked it up for you. It sounds like you are talking about oleander leaf scorch:

https://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7480.html

From the article:

Oleander leaf scorch is a disease found mainly in southern California.

Your intro says you are in SoCal. [incidentally please put your location in your profile so it will show, so we don't have to keep going back to your intro to find it]

Leaves on one or more branches may yellow and begin to droop; soon the margins of the leaves turn a deeper yellow or brown, and the leaves eventually die. As the disease progresses, more branches of the plant are affected and the plant dies. yellowing of leaves progresses from the tip or margins of leaves inward.


It is a bacterial disease, spread from plant to plant by leafhopper insects, particularly sharpshooter leafhoppers.

The news does not sound good

There is no known cure for oleander leaf scorch. Pruning out the part of the plant showing symptoms may help the appearance of the oleander tree or shrub but will not save the plant. The bacteria by then have already moved throughout the plant via the xylem, and limbs that show symptoms are only the first to become affected. Research indicates that some cultivars of oleander may express symptoms to lesser degrees than others and may live longer than other varieties when infected.

Because of the year-round abundance of the glassy-winged sharpshooter, currently available insecticides are not effective in stopping the spread of the disease. The best management may be early removal of plants infected with the oleander leaf scorch bacteria to reduce the source of inoculum, but there are no experimental data to validate this method.

I had not heard of this before. It is very sad. I think of all the miles and miles of oleander up I-5 and other freeways. I wonder if they are all doomed. The article says this is another newly introduced disease that is spreading all over the place and will not stay limited to SoCal. Pity all the creatures of the earth over whom [some say] we were given dominion.

Given the doomful sound of all this, it is hard to make any suggestions for you. I would get rid of any diseased bushes immediately to try to protect your remaining ones.

Here's an article about natural enemies of leafhoppers:

https://www.ipm.ucdavis.edu/PMG/C302/m30 ... enemy.html

It is about the grape leafhopper, but I'm sure it is similar for others.

This article is about your particular sharpshooter leafhopper:

https://www.ipm.ucdavis.edu/PMG/C302/m30 ... enemy.html


If you scroll down near the bottom, past a bunch of really ugly photos, to the part about Natural Enemies it says:

The natural enemies of sharpshooters include predatory insects such as mantids and dragonflies. Free living and snare-building spiders also capture and eat sharpshooters. In Florida, anoles have been observed eating sharpshooters. Small parasitic wasps in the genus Gonatocerus are important natural enemies of sharpshooters because they attack the egg stage of several species

Mantids are praying mantises. Praying mantises and ladybugs can be ordered on line. Trichogamma wasps are one variety of the parasitic wasps, genus gonatocerus, mentioned. They can also be ordered:

https://www.planetnatural.com/product/tr ... OgodDAkAnw

I have found in my garden that parasitic wasps are very effective in controlling pests. To attract them to your garden, keep sources of moisture around, like shallow pans with rocks in them so the wasp has a place to land without drowning. Grow flowers that have nectar in tiny florets like alyssum, cilantro and other herbs from the dill family, and composite flowers such as daisies and asters, chamomile, sedum, wild grape.

Another possibility for controlling the leafhoppers that spread the disease, is to spray your plants [the remaining ones, after you have removed the unhealthy ones] with Neem oil. Neem oil kills in two way - directly if it is sprayed directly on the insect and by ingestion, when leaf eaters ingest it. The topical method will kill any insect it is sprayed on, so you want to be sure that you spray late in the evening after honeybees have gone home and don't broadcast the spray, get it directly on your leaves. After it is dried on the leaves, it will be harmful only to leaf eaters that ingest it and not to any beneficial insects. I don't usually suggest preventative spraying of anything, but in this case, it seems really important to protect your remaining oleander from the bacteria carrying leafhoppers.

Good luck. Hope some of this is helpful and you are able to save some of your oleander!

[wysteriangnome]

Thank you so much, this was helpful. I have noticed a few praying mantis in the gardens, and our local nursery sells them, along with ladybugs, so we will be sure to get lots of them. And I may have to cut back a couple other of our larger plants, in hopes of saving them for awhile. I've noticed the leaf scorch on them, the beginning stages. It's different looking than sun damage. Yes, they are beautiful along the highways. Hopefully the water & dishsoap helps a bit, with cutting back. I will make a note next Spring, if it helps the first one. Thanks again. Now I must go look for my profile, I didn't know I had one.

[wysteriangnome]

Found my profile,
Also noted, the wasps; It seems they are attracted to our pomegrante tree. The bees love the flowering succulents. I will put out the water in rocks, in the garden as well.
Appreciated advice , I dislike pesticides so anything natural is best.

[rainbowgardener]

The wasps you are seeing are not the ones that would parasitize your leaf hoppers. There are thousands of different kinds of wasps - literally. Trichogamma is the genus of the parasitic wasp I mentioned and there are 200 species of them. They are nearly microscopic, maybe 1/50th of an inch or so. You won't see them, but they lay their eggs inside the eggs of the leafhopper or other insects. Their larvae hatch out and eat the insect egg they are in.

Here's an article about how to use them:

trichogamma wasp

I know you hate to sacrifice any of your oleanders, but if the cut ones grow back and still are showing symptoms of the disease, I would get rid of them immediately. I mean cut them down and dig the roots out. This sounds like it is a systemic disease which will be present in all parts of the plant. And it sounds nasty. If it were me, I wouldn't want to take chances with losing all of the oleanders and helping spread it to everyone else's. As it is, the fact that more than one of your shrubs is showing symptoms suggests that possibly it is already too late to save any of them. I'm really sorry to be the bearer of such bad tidings.

[rainbowgardener]

An object lesson in the dangers of monoculture. Whoever decided to put hundreds of miles of oleander in the center divide of freeways created a gigantic oleander monoculture. It is very attractive to disease and pest organisms that like oleander and very vulnerable. And of course the plants have to be a bit stressed baking in the sun in a giant stream of car exhaust. So this disease now that it is here, once it finds the freeway plantings is likely to just race through them, leaving hundreds of miles of dead nothing.

If they had done more diverse plantings, it wouldn't have been so attractive to pests drawing them in from everywhere around, the spread of disease and pest from one to the next would be slowed down a lot by having other kinds of plants in between, and worst case, even if the oleanders died, there would still be other plants there.

No monocultures!

[wysteriangnome]

Yes they sure did plant a ton of them, it would be awful to see them all die. I ordered praying mantis, look forward to getting them in the next couple days. After they grow bigger, I will (spray?) Neem oil. I've never used it but will find out more about application when I get it.
The one bad oleander that I cut back has shown bad scorch on the new growth. Now that I have looked around better, it seems at least 3 more large trees have it as well. What a shame. I will try to dig the one out by the roots; it's huge, but I've done it before for 2 others that had died. Felt like I was digging for a jacuzzi.
I already have a pepper tree newly planted nearby, as that oleander was privacy from the main road at the front of the house. If by next spring the two-three others have not improved, I suppose I will have to do similar.
Off to work I go. Thanks again.

[wysteriangnome]

This is the one that I may have to dig up. I hope the image appears.

[wysteriangnome]

This is my last post on this subject. I have been out trimming then came in and read up a lot on the subject, and found out that in California it has been estimated to have caused damage of approx. $52 million along 2000 miles of freeway. (the Oleanders)

So I guess we don't have much hope, your right.