History of Sweet Orange Scab
Sweet Orange Scab (SOS) is a fungal disease caused by the fungus Elsinoë australis. Sweet Orange Scab is found in many of the citrus growing regions of South America: Argentina, Bolivia, Brazil, Ecuador, Paraguay, Uruguay, and in Korea. In the United States, the disease was believed to have been detected on a residential tree in Texas in 2010. This disease can be easily confused with common Citrus Scab which is found in Florida and caused by a different fungus Elsinoë fawcettii. The host range for Sweet Orange Scab are sweet oranges and tangerines. This contrasts with Citrus Scab which affects, grapefruit, tangerines, and limes, but does not commonly affect sweet orange varieties.
How to Report a Suspected Find
If you suspect you may have Sweet Orange Scab, please contact your local Florida Department of Agriculture and Consumer Service's CHRP office for further diagnostic testing. Do not move infected plant material out of the area.
Fruit, Leaf, and Stem Symptoms
Young fruit exhibit wart-like pustules, which are tan to gray in color, raised, corky, and rough to the touch. As the fruit matures the lesions become smoother. Fruit infected with SOS cannot be sold for the fresh market because of appearance. They can be sold for juice because the internal quality if the fruit is not compromised by this disease Unlike Citrus Scab, Sweet Orange Scab does not exhibit symptoms on the leaves and twigs, only on the fruit.
Spread
The presence of moisture is necessary for Elsinoë australis to produce spores and spread. The asexual spores (conidia) are produced in lesions on the fruit and are spread short distances by rain splash. The movement of infected fruit out of quarantine areas causes the fungus to travel long distances. The fungus also requires the presence of susceptible young fruit, which are susceptible from 6-8 weeks after petal fall. Unlike the spores of Elsinoë fawcettii which survive in old leaves and twigs, it is not known how the spores of Elsinoë australis survive in the absence of susceptible fruit, but infections can still occur the following season even when all fruit are removed.
Regulations and Management
Do not use overhead irrigation, as this can cause the fungal spores to be carried in by water drops and spread from fruit-to-fruit. The use of azoxytrobin, trifloxystrobin, pyraclostrobin, ferbam, and copper fungicides create a barrier on the fruit during its most susceptible growing period, reducing the amount of inoculum. A typical spray program for areas infected with SOS is for two fungicide sprays: one at 2/3rd petal fall and a second spray applied 2-3 weeks later. Educational resources and identification tools should be utilized by grove workers, managers, and other industry professionals to increase awareness and knowledge of this disease. If you suspect the presence of SOS in your grove, do not move the fruit out of the area.
Photo Gallery
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Links
Resources
If you would like to obtain laminated identification sheets or copies of the other various educational materials, please contact Jamie Burrow, 863-956-8648 or jdyates@ufl.edu
Contacts
For questions, please email crec-web@ifas.ufl.edu
