Citrus greening or Huanglongbing (HLB) 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 commercial citrus-producing areas leading to a remarkable 75% decline in Florida’s $9 billion citrus industry (USDA).
In the Panhandle, UF/IFAS Extension Agents have implemented a survey to track and monitor citrus greening, including evidence of the vector, the Asian Citrus Psyllid (ACP), which depending on individual, may or may not carry the disease. Confirmed cases of citrus greening in the Panhandle have been isolated to Franklin County to date. Although, there has been a positive identification of the ACP in seven northern counties, including Gulf and Bay.
The ACP nymphs are yellow-green in color and will produce a white, waxy substance or tubules (Fig. 1). 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.
So, what are the symptoms? Citrus greening will lead to yellowing of the leaves along the veins. A green tie-dye look to the leaves is a typical sign. Fruit will be asymmetrical and dark green on the end. To make matters worse, it’s difficult to diagnose, especially during non-fruiting months, where leaves are only the symptomatic feature. Symptoms can easily be confused with nutrient deficiency. Lab analysis is most likely needed to identify. Fruit production will also 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. However, it is known that the most severely affected citrus are sweet oranges, mandarins and mandarin hybrids.
What can I do to help prevent the disease as a backyard citrus grower? Unfortunately, there are no chemical options to treat an infected citrus tree at this point, only methods to keep the condition from spreading from tree to tree. Detection through scouting is the first line of defense. Dr. Xavier Martini of the UF/IFAS North Florida Research & Education Center is studying the distribution and population dynamics of the ACP in northern Florida. His studies have shown that peaks of infestation in flush (new growth) is at its height in summer and fall. This is the time to be particularly vigilant in scouting. Preventative pesticide applications during this time is also recommended. A foliar spray such as a non-systemic pesticide like malathion or neem oil (a less toxic repellant) accompanied by a soil drench containing imidacloprid can help as a deterrent. Please follow the product directions, rates and precautions.
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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