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Last week, I was visiting one of my favorite clients when I noticed that one of her citrus trees was showing signs of sunburn, which led to me explaining to her that even citrus trees need sunscreen to prevent sunburn in many cases.

You can see the lighter-colored bark and some cracks as well along the branch. It turns out that citrus trees are very susceptible to sunburn.
 
So, why is a sunburned citrus tree something to be worried about?
 
Well, when a tree becomes sunburned, it often forms cracks in the bark and within these cracks, damaging insects or fungus can find a nice home.  Frost damage can also cause cracks in the bark.
 
In recent years, I have had to deliver bad news to people whose citrus trees became infected with sooty canker, which is a fungal disease that affects the branches and trunks, which takes root underneath the cracked, flaky bark.
 
 
Several times, I have had to tell homeowners that their much-loved citrus tree was badly infected with sooty canker and had to be removed.  You can read more about the signs and treatment of sooty canker, here.
 
Thankfully, there are things we can do to reduce or eliminate the chance of sunburn to our citrus trees.
 
 
1. Allow citrus trees to grow their lower branches. They will help to shade the trunk.  A bonus for citrus trees grown this way is that the most fruit is produced on the lower branches that also tastes sweeter.
 
 
2. Protect exposed trunks and branches by using citrus paint (available at your local nursery) or by simply mixing white latex paint water so that the resulting mixture is 1/2 paint and 1/2 water. You can also purchase tree wraps made from burlap, which can also help to protect them. Avoid using oil-based paint. 
However, if you allow the lower branches of your citrus tree to grow and the trunk is shaded, than you don’t have to paint them. 
3. Don’t over-prune your citrus trees.  The photo above, is an EXTREME example of what not to do.
 
Citrus trees should be pruned in March, and concentrated on removing dead, diseased or crossing branches.  Avoid pruning more then 20% of its foliage in any given year.  *Remember, that the leaves make food for the tree, which will in turn, produce delicious fruit. If pruning leaves you with exposed branches, then coat them with citrus paint.
**See how to protect citrus from the damaging effects of a heat wave – here.
 
I always wear sunscreen whenever I venture outdoors.  Years spent in California at the beach as a teenager, trying to tan my fair skin did not work.  Now, I try very hard to protect my skin from the desert sun.  I do however, often forget to wear my hat as it does mess up my hair 😉
 
So, do your citrus tree a favor and make sure it is protected from the sun – either by its branches or by ‘sunscreen’.

Most of my job as a horticulturist and garden writer is fun.  

But sometimes, I have to be the bearer of bad news.

Last week, I was called to a home where the homeowners were worried about one of their citrus trees.  Although I am a horticulturist, I am also a Certified Arborist, which can also be very helpful – especially when I am dealing with trees.

There was a large lemon tree in their front garden.  They were concerned because they had some branches dying back and wanted to know what the cause was.

So, I stopped by and took a look at the lemon tree.  At first glance, it looked fine – the homeowner had had the dead branches removed.

But, I had to look more closely, which meant getting close to the interior branches and the trunk.

What I saw in one of the remaining branches wasn’t good…

      
Can you see that the branch on the left is missing bark and is colored black?
What is this you may wonder?
Sooty Canker.
Sooty Canker is a fungal disease that infects many different species of trees including citrus.  It spreads through fungal spores.  The spores enter the tree through damaged areas on the branches or trunk, forming lesions and eventually causing the bark to peel off.
It is called ‘sooty canker’ because of the black color of the fungal spores.  The branches almost looked as if they have been scorched by fire.
In this case, the lemon tree had experienced severe frost damage 1 1/2 years ago.  Frost can cause splitting and other damage in the bark.  Sunburn damage can cause similar problems as wellThe fungal spores enter through these damaged areas and begin to grow.
If only branches are affected, they can be pruned 6 inches to 1 ft. below where you see evidence of the sooty canker.  Pruning tools must be disinfected with a 20% bleach solution to keep the disease from spreading between each pruning cut.
I was hopeful that I could tell the homeowners that all they had to do was to prune the affected branches.
But that was before I looked down at the trunk…
   
The entire trunk was infected with sooty canker.  Unfortunately, this almost certainly means that the tree will die.  
In this case, the tree should be removed to avoid spreading it to other trees.
I hated to tell the homeowners that they would have to have their tree taken out.  Especially after they told me how much fruit they had enjoyed over the years from this tree.
After I told them the fatal diagnosis of their lemon tree – I offered to look at their other four citrus trees.  I wanted to make sure that they weren’t infected as well.
Well, the good news was that their Meyer lemon tree was healthy.
The bad news was that their two orange trees and pommelo tree were all badly infected with sooty canker.  
Did I mention that I hate being the bearer of bad news?
I must say that the clients accepted the bad news very well.
In fact, they said that they had gotten tired of picking up dropped fruit AND that one of them couldn’t even eat citrus any more due to dietary constraints.
They will be removing their five infected citrus trees while keeping a close eye on their disease-free Meyer lemon tree.  At the first sign of a lesion, they will prune it away to help keep it safe from infection.
Guess what?   
They asked me to return in spring to design a new landscape area in place of their citrus trees.  I like being with people who see things as “a glass half-full”.  
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If you suspect that your tree has sooty canker – have a professional confirm the diagnosis and discuss with you the treatment options.  If the trunk is not affected, you may be able to save your tree. 
For more information, check out this link.