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Yellow Bells (Tecoma stans stans)
Do you have caterpillars lurking beneath the leaves of your shrubs?
 
If they look like the yellow bells shrub, pictured above, probably not.
 
 
But, if your leaves look as if a vampire came along and sucked them dry, then they are there, whether you can see them or not. Other telltale signs include little black pellets, which are caterpillar ‘poop’. 
 
Damaged bougainvillea leaves
 
Bougainvillea can also fall prey to hungry caterpillars, who leave behind ragged holes and edges.
 
So, what do you do?  Nothing?  Or should you pull out all the stops to get rid of them?
 
I address these questions and more in my latest video:
 
 

 

What do you do when you see damaging insects such as aphids sucking on your plants?


Do you reach for the nearest bottle of insecticide? Pluck them off or spray them with a hose?  


Believe it or not, sometimes the best thing is to do nothing.  I learned this lesson long ago before I went to school to become a horticulturist.


I remembered this important lesson when I passed by a severely pruned oleander shrub on my way to our weekly bagel lunch after church.  


The oleanders were growing back nicely.  However, there was some yellow aphids on the young leaves.

Years ago, my oleander shrubs had an infestation of yellow aphids like this, and I was anxious to get rid of them.

I had several methods at my disposal – insecticidal soap, a strong jet of water or my fingers – all of which, would help get rid of most of the aphids.  But, life got in the way, and I didn’t have a chance to get out to treat my shrubs until about ten days later.  

Can you guess what I found?  Not a single aphid.  I didn’t have to do a thing, and the aphids were gone, and my shrubs look great.

So, what happened to the aphids?

When harmful insect pests first appear, it can take a week or two before their natural predators follow.  In the case of aphids, lacewing and ladybugs showed up and ate the aphids.  

Plants are tougher than we give them credit for and can handle a certain amount of insect pests without any adverse effects to the plant itself.  

So, when I come back in a couple of weeks to the same bagel shop, I expect to see no aphids in sight and a healthy oleander shrub.

Love them or hate them, oleanders have a firm foothold in the desert landscape where they are usually seen creating living green ‘walls’ in order to provide privacy.  


Their popularity is due in large part to several characteristics:

– Their evergreen foliage provides the rich, dark green color that many miss living in the desert.

– Oleanders are easy to grow, with little to no fertilizer and are drought tolerant once established.

– They add beauty to the landscape spring through fall with their flowers.


While the popularity of oleanders is still holding on, there is a fatal disease that affects them that has made its way from California and is now being seen increasingly in Arizona.

Oleander leaf scorch (Xylella fastidiosa) is a bacterial disease that plugs up the vascular system of affected oleanders, eventually making the movement of water throughout the plant impossible over time.

This disease is spread by flying insects, called sharpshooters.   These small insects (1/4 inch long) become carriers of the disease when they feed upon an infected oleander.  Thereafter, they spread it to every other oleander they feed upon.

Oleanders in Southern California were first diagnosed with the diease in the early 90’s and it was just a matter of time before it spread to Arizona.  

Advanced stages of oleander leaf scorch

Oleander leaf scorch was first diagnosed in Arizona in 2004.  Its spread has been slow, but inexorable.  

I have seen several cases of this disease during landscape consultations, including one that I did yesterday.


The homeowner had a very large oleander hedge that was over 20 years old, which provided privacy from his neighbors.

What may look like some browing leaves in this small branch is one of the classic symptoms of oleander leaf scorch.

Oleander leaf scorch
Close up, you can see the brown, outer leaf margins, which is characteristic of oleander leaf scorch.  (Not to be confused with drought symptoms, which cause discoloration of the middle of the leaf).

As we continued to walk along the row of oleanders, the infected oleanders were interspersed between healthy ones.  The reason for this is that the nature of flying insects is that they hop from one plant to another, but not necessarily the next plant – they may fly 3 shrubs away before feeding again or to the next yard or block.

Symptoms of oleander leaf scorch
This oleander showed another type of browning symptom of oleander leaf scorch with the tips looking ‘scorched’.  

It’s important to note that salt burn resulting from drought or shallow irrigation can cause similar symptoms as shown in the photo below:

Drought-stressed oleander leaves

Note the middle of the oleander leaf is affected in the case of drought stress.  While unsightly, the oleander pictured above, does NOT show signs of oleander leaf scorch.

Initial signs of oleander leaf scorch.

Back to the oleanders showing signs of oleander leaf scorch – by looking closely at seemingly healthy oleanders, I could see the beginning of symptoms with lighter green alongside darker leaves.  The signs of the disease don’t show up all at once in the beginning.  Often, it starts out with a branch here and there showing signs initially that will gradually progress throughout the entire plant.

It’s important to note that once an oleander has been infected with this disease, the entire plant has it – not just the branches that initially show the first signs.

Lower leaves showing the beginning symptoms of oleander leaf scorch.

So, what is the treatment for oleander leaf scorch? Sadly, there is no cure and it will eventually kill oleanders over a 3 – 5 year period once infected.

Some experts recommend pruning out affected branches to improve the appearance of infected oleander shrubs for the short term.  But, they will die.

I recommend removing infected oleanders right way to help keep the disease from spreading.  
Personally, I have seen the disease affecting large, old oleanders in North Central Phoenix and in the Arcadia area.  It’s simply a matter of time before I will see it in outlying areas.  

Initial signs of oleander leaf scorch

Consult with an expert if you suspect that your oleanders are infected.  Problems with irrigation, nutrient deficiency and salt burn can mimic some of the symptoms of oleander leaf scorch and a horticulturist or other landscape expert can help you rule out other causes.  Ultimately,
positive identification of oleander leaf scorch can only be made by a lab tests through your local cooperative extension office.

Can you can simply get rid of infected oleanders and start over with new ones?  The anwer is, “no”.  The reason for this is that the disease is already present in the local sharpshooter insect population and it is only a matter of time before the infect your new oleander shrubs.

I recommend using hop bush (Dodonaea viscosa) as an alternative to oleanders.  It is evergreen, recommended for use near pools, makes a great hedge, is drought tolerant and attractive.
For more information on oleander leaf scorch, you may want to check out the following links:



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I hope your day is off to a great start!  I’m off to the Desert Botanical Garden’s spring plant sale.  I just hope my car has enough room to fit all the plants I will want to buy 🙂