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Searching for the answer to citrus greening

Ray Bodrey Gulf County Extension Director UF
IFAS Special to The Star
The Star

Citrus greening or Huanglongbing (HLB) is 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 in 2005. Since then, the disease has affected most commercial producing areas in Florida and California. Commercial citrus producers in Florida have seen a remarkable 75 percent decline in the State’s $9 billion citrus industry (USDA).

In recent years, 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 insect, may, but may not carry the disease. Confirmed cases of both the ACP and citrus greening have been found in many counties of north Florida, including Gulf.

The ACP nymphs are yellow-green in color and produce a white, waxy substance or tubules (figure 1). The adults are small, approximately 1/8” and are brown in color (figure 1). 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, with a steady decline in health to follow.

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.

No citrus species is immune to the bacterium and until recent, no viable treatment options were available for backyard citrus and limited results with antibiotics and pesticides for commercial groves. However, the recent conclusion of a five-year study conducted by the University of California-Riverside could offer promising hope. Researchers have uncovered an effective treatment by utilizing antimicrobial properties of wild citrus relatives. The treatment in spray form should be available in the near future.

What can you do to help prevent the disease as a backyard citrus grower? 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 for the insect. It is also recommended that preventative insecticide sprays be applied during this time. 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 of the insect vector. Please follow the product directions, rates and precautions.

For more information, contact Gulf County Extension at 639-3200 or email at rbodrey@ufl.edu.

*Due to COVID-19, our physical office location is closed to public traffic at this time. However, please call or email us for assistance with extension related needs. Sorry for the inconvenience.

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 and at the UF/IFAS Entomology website, http://entomology.ifas.ufl.edu/creatures/citrus/acpsyllid.htm.

UC-Riverside article: https://news.ucr.edu/articles/2020/07/07/uc-riverside-discovers-first-effective-treatment-citrus-destroying-disease

UF/IFAS Extension is an Equal Opportunity Institution.