Huanglongbing (HLB), also called citrus greening, is one of the most threatening diseases to citrus plants in the U.S. and worldwide. The HLB bacterium is spread by the tiny, invasive Asian citrus psyllid and may infect a wide range of citrus and closely related species. The disease is fatal, and presently there is no known cure.
HLB has the potential to devastate the U.S. commercial citrus industry by killing plants and rendering fruits bitter and unmarketable. HLB was first detected in Florida in 2005, and by 2018, it had also occurred in California, Georgia, Louisiana, Puerto Rico, South Carolina, Texas and the U.S. Virgin Islands. In the five years following its initial U.S. detection, HLB caused the loss of over 8,000 jobs, $2.7 billion in citrus industry revenue, and $4.5 billion in total economic output in Florida alone. In some states, these steep costs of combatting—and succumbing to—HLB make preventative measures and early detection essential to survival of the citrus industry.
The Huanglongbing bacterium is spread by a tiny, invasive insect, the Asian citrus psyllid (ACP). This tiny psyllid inflicts additional harm directly to citrus plants, stunting and deforming new growth as it extracts sap from the plant. However, this harm is minor in comparison to the fatality caused by the disease it spreads.
Source: Hodges, A. W. and T. H. Spreen. 2012. Economic impacts of citrus greening (HLB) in Florida, 2006/07 to 2010/2011. Institute of Food and Agricultural Sciences, University of Florida. Document FE903. 5 pp. www.crec.ifas.ufl.edu/extension/greening/PDF/FE90300.pdf
The Asian citrus psyllid is an extremely efficient vector; its dependency on citrus plants throughout its lifecycle ensures effective disease transmission. ACP contract the HLB bacteria by feeding on infected plants, then retain the ability to vector the disease for the remainder of their lifespan.
HLB also spreads when infected plant material is moved to new locations. Although distribution of commercially packaged fruit is not known to spread citrus greening, plants and cuttings may introduce the infection to new areas. To minimize this risk, review federal and state regulations and quarentines before purchasing or transporting any plant material, and ask whether the vendor is in compliance. If you grow citrus at home, don't move plant material even if no psyllids are visible!
ACP feeds on wide range of citrus and closely related species, and HLB may be contracted by many of these plants—even your backyard trees! Crops like oranges, grapefruit, limes, and lemons are susceptible to the direct impact of ACP as well as HLB infection, making the commercial citrus industry vulnerable to the impact of this pathogen complex.
Characteristic yellow-blotched leaves and lopsided green fruits of infected plants may be easily detectable, but the disease is fatal once these symptoms become visible. To more effectively deter the spread of citrus greening, monitor the undersides of citrus leaves for the 3-4mm long Asian citrus psyllid (ACP), the insect which transmits this bacterial infection between plants. Detection and reporting of these symptoms is our first line of defense against this potentially devastating disease. Other signs and symptoms include:
- Asymmetrical, blotchy mottling of leaves
- Stunted, sparsely foliated trees that may bloom off-season
- Fruit that remains green even when ripe
- Yellow shoots & twig dieback
- Lopsided, bitter, hard fruit with small, dark aborted seed