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Citrus Leprosis is a virus found in South and Central America. The virus is spread by spider mites in the genus Brevipalpus and the symptoms on the tree are only present where the mite has fed. If the infestation of mites is heavy there can be severe loss of fruit and overall tree decline.
This mite is very small - the green surface you see is a leaf under the mite in this image. Mites are piercing feeders and reproduce by laying eggs. Chemical control of mites is difficult because the mite will hide in cracks and crevices of the tree bark, in leaf axils and other places a sprayed chemical will not "reach". Miticides are also expensive.
As the mite feeds the virus lesions form on the plant. On the leaves the symptom is a chlorotic ring spot that will eventually develop a necrotic (dead) center point.
The fruit develop a circular lesion as well. Lesions on twigs can almost look like a scale insect, and if there are enough of these lesions on a twig there may be dieback of that twig or branch. Twig image courtesy of Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [April 2013] .
Sweet oranges are very susceptible to the virus. Under the high magnification of Electron microscopy there appear to be 2 forms of the virus within the cells. Both are rod shaped but are found in different parts of the plant cell.
Most likely, as with all citrus diseases, Leprosis is spread by hitchhiking mites on transported citrus or are windblown field to field.
There have not been any major outbreaks of this virus in the US in recent years. In Brazil 35% of fruit production cost is spent on Miticides. The mite, but not the virus, is already present in our citrus growing regions here in the USA.
For more information about citrus pathogens please contact Dr. John Hartung
For more information concerning growing citrus please contact Cristina Paul