Scalybutt is a disease of citrus tree bark. Also known as exocortis, scalybutt is a virus-like disease caused by a particle, not a virus, called the Citrus exocortis viroid (CEVd).
Viroids are the smallest known infectious pathogens, made of a single, naked RNA strand. Other diseases caused by viroids include potato tuber spindle disease, avocado sunblotch, and peach latent mosaic.
Scalybutt used to be a serious threat to citrus trees, especially those grown with Trifoliate rootstocks, but strict regulations and agricultural inspections have reduced the likelihood of scalybutt 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 uninfected trees.
Symptoms of scalybutt
If you see drying, cracking, and lifting bark, it may be scalybutt. Damaged bark may also peel away from the tree trunk in thin strips in a behavior called shelling. Of course, these are the same symptoms of sunburn damage, so how would a gardener know the difference? For one thing, you may also see gum droplets under the loose bark or stunting. Stunting occurs because nutrients have difficulty moving through damaged or exposed vascular bundles. Sunburn damage generally does not cause stunting or gummosis.
Dealing with scalybutt
You can’t cure scalybutt, and it is highly contagious. But it probably won’t kill your tree. It will reduce harvests and make the tree susceptible to other pests and diseases. 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.
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