Exocortis

Exocortis is a virus-like disease of citrus tree bark. I say virus-like because it is caused by a particle, not a virus, called the Citrus Exocortis viroid (CEVd). 


Viroids are the smallest known infectious pathogens, made up of a single, naked strand of RNA. Other diseases caused by viroids include potato tuber spindle disease, avocado sunblotch, and peach latent mosaic.

Exocortis used to be a serious threat to citrus tress, especially those grown with Trifoliate rootstocks, but strict regulations and agricultural inspections have reduced the likelihood of exocortis affecting your citrus trees. That is, if your trees are relatively young. Older trees (>40 years) may still be infected. This is important because you don’t want to spread exocortis viroids to uninflected trees.


Symptoms of exocortis
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If you see drying, cracking, and lifting bark, it may be exocortis. Damaged bark may also peel away from the tree trunk in thin strips. This is called shelling. Of course, these are the same symptoms of sunburn damage, so how would a gardener know the difference?

Exocortis kills the bark of citrus trees (UCANR)

Stunting is one symptom of citrus exocortis (UCANR)

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For one thing, you may also see gum droplets under the loose bark, or stunting. Stunting occurs because nutrients are having a difficult time moving through damaged or exposed vascular bundles. Sunburn damage generally does not cause stunting or gummosis.


Dealing with exocortis

You can’t cure exocortis and it is highly contagious. That being said, it probably won’t kill your tree. What it will do is reduce production and make your tree susceptible to other pest and disease problems. Unless you are ready to commit to complete sanitation of shoes, tools, and anything else that might come into contact with an infected tree, its removal is your best option, if only to protect neighboring trees.