AUBURN, Ala.—Agriculture officials have identified new cases of sweet orange scab (SOS) in Baldwin County. SOS was first confirmed in Alabama in December 2017.
Dr. Kassie Connor, an Alabama Extension plant pathologist, said the disease may have been pushed into the state by strong weather systems.
“We suspect the pathogen spread from Florida via hurricane movement last year,” said Conner. “The pathogen may be widespread, but undetected in other locations at this time.”
Originally, officials found sweet orange scab in Baldwin County while the state was conducting a survey for another disease threatening citrus, citrus greening disease. The Auburn University Plant Diagnostic Lab made the initial diagnosis of SOS which was confirmed by the U.S. Department of Agriculture.
Caused by the fungus Elsinöe australis, sweet orange scab gets its name from the scab-like lesions on the outside of the rind of citrus fruit. While the fruit has distinct symptoms, the tree foliage damage is not heavy by SOS. The symptoms on leaves are inconspicuous.
Connor said that SOS causes concerns for producers that grow for the fresh market.
“This is a federally regulated pathogen of citrus. It only affects the fruit causing corky, wart-like pustules,” said Connor. “The damage is superficial and does not affect the inside of the fruit or the taste; however, it is a significant problem on fresh market fruit producers.”
Connor said that detection of SOS, as well as citrus greening, in Alabama will have quarantine implications for marketing of fresh fruit.
The fungus requires moist conditions to reproduce and spreads primarily by splashing water and wind. People can also spread the disease by moving infected nursery stock or fruit.
Conner encourages growers to spray fungicides in advance but only if timed correctly. Symptoms will not be present until the fall and spraying is only to protect fruit from infection. Producers can use products containing the active ingredients azoxystrobin, trifloxystrobin, pyraclostrobin, ferbam and copper fungicides.
These fungicides create a barrier on the fruit during its most susceptible growing period, reducing the amount of inoculum for infection. Producers should make two fungicide applications: one at two-thirds petal fall and a second spray two to three weeks later.