Huanglongbing (HLB) or “citrus greening” is currently the most devastating disease of citrus worldwide
Huanglongbing (HLB) or “citrus greening” is currently the most devastating disease of citrus worldwide. The disease was first reported in 1919 in China, and again in Brazil in 2004 and discovered in Miami, FL in 2005. Since then, the disease has affected most of Florida’s citrus-producing areas leading to a remarkable 75 percent decline in Florida’s $9 billion citrus industry (USDA).
In the Panhandle, citrus greening was suspected in December of 2016 at a residential property in Carabelle. Shortly thereafter, the sample was positively identified as citrus greening by the UF/IFAS North Florida Research & Education Center - Plant Disease Diagnostic Clinic. After the positive identification, the Florida Department of Agriculture and Consumer Services Department of Plant Industry (FDACS DPI) confirmed the finding as a new county official record. Other cases in the Panhandle have been reported as of recent.
Citrus greening is a particularly difficult disease to identify and manage. The vector is known as the Asian Citrus Psyllid. The psyllid has an accelerated life cycle (Fig. 1). The nymphs are yellow-green in color and will produce a white, waxy substance. The adults are small, approximately 1/8” and are brown in color. The Asian psyllid is not directly the cause of the citrus tree demise as it attacks the truck, branches, leaves or fruit. More so, the bacteria that is released from the psyllid during the attack is cause of the condition. The bacterium will live and thrive in the tree’s phloem for some time. The phloem is the living tissue of the tree that transports nutrients throughout. However once infected, the phloem will transport the disease to other parts of the tree. Unfortunately, once infected, the tree will steadily decline in health. Fruit production will drop in number, size and taste each year until the demise of the tree. Sadly, there is no cure, nor citrus species that is immune to the bacterium. It is known that the most severely affected citrus are sweet oranges, mandarins and mandarin hybrids.
Symptoms of citrus greening often begin by the yellowing of the leaves along the veins. A green tie-dye look to the leaves is a typical sign (Fig. 2). To make matters worse, it’s difficult to diagnose. These symptoms can easily be confused with nutrient deficiency. Lab analysis is most likely needed to identify. There are no chemical options to treat the tree at this point, only methods to keep the condition from spreading from tree to tree. A non-systemic pesticide like malathion or neem oil, a less toxic repellant, can help combat the spread of the disease.
So, what should a grower do if a citrus tree is suspect of this condition? Since the entire state of Florida is under quarantine, FDACS DPI officials have stated that currently there are no regulations for infected dooryard citrus. However, shipments of any citrus tree or fruit outside of the state is prohibited. If positively identification is done, it is recommended to remove the tree to avoid further spread of the disease to nearby healthy trees. Applying herbicide to the stump is also essential. Citrus growers in the area should be familiar with the symptoms of citrus greening and monitor their trees routinely as early detection will slow down further spread of the disease by removal of infected trees and control of the insect vector.
Citrus greening is a serious condition that threatens Florida’s citrus crop production as well as dooryard gardeners. Controlling the source of the bacterium is extremely important. Keep in mind that the most common vector regarding the spread of these diseases is humans transferring citrus from one region to another. If you suspect that your citrus trees may have this condition, please contact the FDACS Division of Plant Industry’s Helpline Center at 1-888-397-1517 before taking any action to reduce accidental spread of this disease. For more information, please visit the UF/IFAS Entomology website, http://entomology.ifas.ufl.edu/creatures/citrus/acpsyllid.htm.
Gulf County Extension is participating in a study to track the occurrence of the disease and vector. If you are a Gulf County resident with citrus trees and wish to participate in the study, please call 639-3200.
Supporting information for this article supplied by X. Martini, M. Paret, P. Andersen, L. Stelinski, F. Iriarte, I. Small, N. Nguyen, M. Dewdney, E. Johnson and E. Lovestrand, all affiliated with UF/IFAS Extension.
Other supporting information can be found in the UF/IFAS EDIS publication, “Citrus Problems in the Home Landscape” by Mongi Zekri and Robert E. Rouse: http://edis.ifas.ufl.edu/hs141
& “Citrus Canker & Greening (HLB) – Handling Protocols for Master Gardener Plant Clinics” by Megan M. Dewdney, Timothy M. Spann, Ryan A. Atwood, Jamie Burrow: http://edis.ifas.ufl.edu/pdffiles/HS/HS37100.pdf
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