By Danielle Sprague
Scouting for citrus greening disease or huanglongbing (HLB) should be an essential practice of citrus growers in our area. The symptoms of this disease can be found year round, but they are most visible now through March. Citrus greening affects all varieties of citrus and is widespread throughout the industry in South Florida. Disease incidence in the Panhandle is low, therefore, scouting and infected tree removal is still a valuable production practice.
Citrus greening is a bacterial disease caused by the bacteria Candidatus Liberibacter. The bacterium is spread from tree to tree by an insect known as the Asian citrus psyllid. Psyllids spread the disease by feeding on infected trees and moving on to non-infected trees. Once a tree is infected, there is little hope for survival as there is no cure for citrus greening.
Symptoms of citrus greening may not always be clear and can be difficult to distinguish from other tree problems. When scouting for greening, look for trees that do not appear normal and examine these trees carefully. A tree infected with citrus greening will appear unhealthy with discolored leaves, a thin canopy, and reduced fruit production.
On severely infected trees, leaf drop, shoot die back, and fruit drop occurs. Fruit may be small, misshaped and/or have an abnormal color change. Fruit may also have an off flavor.
Scouting for citrus greening should be done at least four times a year, or more in areas known to have infected trees. The symptoms are most visible through the fall and winter months, but can be seen year round. As trees begin to flush in the spring, scouting becomes more difficult because new leaves do not typically express symptoms and older, symptomatic leaves become hidden in the tree canopy.
Methods of scouting include visual inspection of trees by walking through groves or riding on all-terrain vehicles (ATVs). Walking the grove will allow for the most thorough inspection, however size of the trees and acreage will determine the most practical method for a grower.
Any suspect trees should be marked with flagging tape. On the flagging tape, include the date and the person scouting’s name. After a row is scouted, marking trees on each end of the row with flagging tape will assist with relocating trees later.
Citrus greening cannot be diagnosed by symptoms alone. Suspect trees that have been flagged should be sampled and sent to the lab to be positively identified by the polymerase chain reaction (PCR) method. There are several labs throughout the state that are able to receive and diagnosis samples. Another method of detection being used more recently are scent detecting dogs.
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