During a training session in City Park in New Orleans, LSU AgCenter extension agents studied trees that exhibited symptoms of citrus canker and citrus greening. Left to right are Lee Rouse, Mariah Bock, Sarah Bertrand, Sandra Benjamin and Craig Roussel. Photo by Raj Singh

Grapefruit leaves exhibit blotchy mottling of leaves when infected with citrus greening. This photo was taken in March 2014 in the New Orleans area. Photo by Raj Singh

This is a sweet orange tree infected with citrus canker in New Orleans. The photo was taken on June 9, 2014, by Raj Singh, director of the LSU AgCenter Plant Diagnostic Center.

News Release Distributed 07/08/14

BATON ROUGE, La. – Citrus harvest is still months away, but this year’s crop in Louisiana faces two growing threats – citrus canker and citrus greening.

Citrus canker, an incurable bacterial disease, was recently found in St. Bernard Parish, said Raj Singh, director of the LSU AgCenter Plant Diagnostic Center. It is present in four other southeastern Louisiana parishes, including Plaquemines, which produces the most citrus in the state. The other three parishes are St. Charles, Jefferson and Orleans.

The canker bacterium causes lesions on all above-ground plant parts, including leaves and fruit. Fruit with canker lesions loses its market value, and, ultimately, infected trees stop producing fruit, Singh said.

All citrus varieties are susceptible. The canker is highly contagious – and warm weather, rain and wind cause it to spread even faster.

“It is going to continue to spread in Louisiana because we have the right weather conditions,” Singh said.

The disease was first detected in Louisiana in 1914, but was eradicated by 1940. In June 2013, citrus canker resurfaced in Louisiana.

Singh said inspectors with the Louisiana Department of Agriculture and Forestry will collect samples from suspected trees in citrus-producing parishes that he will test. While there is not much that can be done once a tree is infected, LDAF quarantines will be put in place to control movement of affected plant material, including fruit.

Singh expects the canker’s growing presence to have a bad effect on this year’s citrus harvest. Fruit from infected trees is safe to eat but difficult to sell because of the unsightly lesions and restrictions from quarantines.

Unfortunately, another incurable bacterial disease called citrus greening was detected in the New Orleans area in March, Singh said. Citrus greening is spread by the Asian citrus psyllid insect. Infected trees produce green bitter fruit and can eventually die.

To help identify these diseases, Singh conducted training sessions for 15 extension agents from southeastern and southwestern Louisiana on May 29 and June 9 in New Orleans. The agents studied trees that exhibited symptoms of citrus canker and citrus greening.

“The symptoms produced by citrus greening are somewhat similar to nutritional deficiencies and can easily be misdiagnosed,” Singh said. “Citrus greening is confirmed by molecular analysis, but if the agents are familiar with the type of the symptoms, they can easily screen them for their constituents.”

Similarly, a fungus called greasy spot may be easily confused with citrus canker, Singh said. The training provided agents experience in identifying both diseases in the field, he said.

In 2013, the Louisiana citrus industry was valued at $5.4 million. There are more than 400 producers in the state.

Olivia McClure