Citrus exocortis is a disease that impacts some citrus trees, particularly those of a specific rootstock known as trifoliate. If you don’t have that rootstock, your trees are most likely safe but there is still a possibility they can be infected. Use clean rootstock to prevent citrus exocortis in your yard, as there is no treatment for the disease.
What is Citrus Exocortis?
Citrus exocortis, also known as scalybutt disease, was discovered in 1948 and was recognized mainly as a bark shelling disease. It kills bark and causes it to dry out, crack, and then lift off the tree in thin strips. This is known as shelling. It mostly occurs on citrus trees with trifoliate rootstock, although it may affect other types.
The causes of citrus exocortis are viroids, pathogens that are even smaller and simpler than viruses. The viroid spreads from one infected budwood to another, most often through tools like pruning clippers.
Citrus exocortis symptoms include the shelling of the bark, which often occurs at the base of the trunk, and stunting of the tree’s growth. These are the main signs of the disease. Depending on the type of citrus tree, there may be other symptoms, such as spots on the leaves, yellowing leaves, or yellow spots on twigs.
The disease does not affect the quality of citrus fruit, but because it stunts growth, it can reduce yield a little bit.
How to Treat Citrus Exocortis
Unfortunately, scalybutt disease cannot actually be treated, but it can be prevented or managed. Prevention is as easy as choosing trees that re-certified to be disease free. This means that the nursery that grafted the tree used clean budwood and rootstock.
If you do see signs of the disease in your home orchard, you can still harvest a decent yield of citrus of high quality. You should, however, take care to prevent the disease from spreading to other trees. Equipment used to prune needs to be disinfected with bleach after working on an infected tree. Heat does not kill the viroid.