Taken from the meaning of the Chinese name for this disease, Huanglongbing (HLB) is the malady we commonly call citrus greening in this country. Many scientists and citrus lovers alike had hopes that our Panhandle location would be spared due to our cooler climate and the fact that an insect, the Asian citrus psyllid, is the primary vector for the disease.
However, HLB has now been diagnosed from citrus samples collected in both Carrabelle and Apalachicola. The presence of an established population of the psyllids has yet to be determined though.
The microscopic bacterium, named Candidatus Liberibacter asiaticus, is the culprit that does the damage and causes the decline of infected trees, which at this time includes all varieties of citrus we grow. The disease has devastated the citrus industry worldwide.
This tiny bacterium lives and multiplies within the phloem tissue of susceptible plants from the leaves to the roots. Damage is caused by an interruption in the flow of food produced through photosynthesis. Infected trees show a significant reduction in root mass even before the canopy thins dramatically. The leaves eventually exhibit a blotchy, yellow mottle that usually looks different from the more symmetrical yellowing pattern caused by soil nutrient deficiencies.
Psyllids feed by sucking juices from the plant tissues and can then transfer bacteria from one tree to another. HLB has been spread through the use of infected bud wood during grafting operations also. One of the challenges with battling this invasive bacterium is that plants don’t generally show noticeable symptoms for perhaps three years or even longer. As you would guess, if the psyllids are present they will be spreading the disease during this time.
Strategies to combat the impacts of this industry-crippling disease have involved spraying to reduce the psyllid population, actual tree removal and replacement with healthy trees, and cooperative efforts between growers in citrus producing areas. You can imagine that if you were trying to manage this issue and your neighbor grower was not, long-term effectiveness of your efforts would be much diminished.
Production costs to fight citrus greening in Florida have increased by 107 percent over the past 10 years and 20 percent of the citrus producing land in the state has been abandoned for citrus. Protecting backyard trees is even more difficult as most owners do not recognize the symptoms and are not likely to implement or be consistent with aggressive management strategies.
A team of plant pathologists, entomologists, and horticulturists at the University of Florida’s centers in Quincy and Lake Alfred and extension agents in the Panhandle are now considering this new finding of HLB to help devise the most effective management strategies to combat this tiny invader in North Florida. With no silver-bullet-cure in sight, cooperative efforts by those affected are the best management practice for all concerned. Vigilance is also important.
If you want to learn more about HLB contact your local UF/IFAS Extension office. If you have citrus trees that seem to be in decline (thin canopy, branches dying back, fruit dropping early), and show the classic blotchy mottle your local extension agent would be interested in seeing them also. Call the office at 653-9337 and ask for Erik.
Erik Lovestrand is the UF/IFAS Franklin County extension director and Florida Sea Grant agent.