Huanglongbing (HLB), also known as citrus greening, is an extremely destructive disease. HLB was first observed in China more than 100 years ago and now is, by far, the most serious threat to the citrus industry worldwide. It is currently jeopardizing the commercial viability of the citrus industry in the United States.
HLB is caused by a phloem limited bacterium Candidatus Liberibacter asiaticus (CLas) and is vectored by an insect, the Asian Citrus Psyllid (ACP). HLB causes many symptoms; early in the disease leaves develop a blotchy, mottle. Later, fruit is dropped prematurely and the few fruit that do develop are small, misshapen, yellow and bitter. The canopy and roots dieback and eventually the tree dies. HLB- infected trees become unproductive within 2 to 4 years after the onset of the disease and young trees that become infected typically do not reach a productive age. There is no cure and all types of citrus and cultivars are affected - oranges, lemons, grapefruit, mandarins, tangerines and others.
Growers, nurseries, scientists and the government are diligently working to slow the spread of this disease, but they cannot do it without your help. It is incredibly important to remove trees that have tested positive for HLB. Every infected tree has the potential to spread the disease to healthy trees, increasing the spread of the disease within and across citrus orchards and residential properties. It is in the best interest of the public and the citrus producers, small and large, conventional and organic, to remove and properly dispose of infected trees.
Huanglongbing (HLB) symptomatology. A) Yellow shoot. B) No
symptoms. Citrus leaves from HLB negative trees. C) Blotchy mottle. Citrus leaves from HLB positive trees with yellow discolorations appearing in nonsymmetric patterns. D) No symptoms. Citrus crop from HLB negative trees. E) Citrus greening. Citrus crop from HLB positive trees with uneven fruit
coloration and the reduced fruit size. F) No symptoms; normally maturing citrus fruit with color break (orange) initiating at the stylar end progressing upwards to the green stem area of the fruit. (G) Color inversion. HLB affected fruit with color break inverted with stylar end (arrow) remaining green while the stem area of the fruit is already orange. H) Lopsided fruit; longitudinal section of deformed HLB affected citrus fruit. I) Lopsided fruit
and aborted seeds; cross section of deformed HLB affected citrus fruit with aborted seeds (arrow). Photos by G. Vidalakis and S. Halbert.
Economic Impact of HLB
The effect of HLB on citrus production and economy can be assessed in three primary ways: 1) increase in mortality rates of infected trees; 2) reduction of marketable yield per tree; and 3) increased cost of production. HLB impact is dependent on several other variables including age of tree at first infection, levels of tolerance, and environmental factors. These variables may allow some trees to maintain the same or similar levels of productivity several years post-infection, while others may decline rapidly.
When the disease was identified in additional locations within the US, nurseries were required to move their production under insect protective structures. In addition, frequent (in some cases every 7 to 15 days) pesticide treatments for vector control in the field were mandated, resulting in a great increase in pesticide use, fuel and labor costs. Indirect costs have also increased due to pesticide-induced disruption of integrated management programs, including biological control, for other citrus pests. In addition, a costly eradication program was instituted to remove infected trees to protect the citrus industry. The economic impacts of HLB in the US over the period 2012-13 through 2015-16 are estimated at a loss of $4.4 billion in cumulative industry output, or an annual average loss of $1.1 billion.
Impact of HLB in California
Currently, HLB has not been found in commercial citrus orchards. However, this ‘good luck’ is not expected to last. HLB has been found in over 1,650 trees in urban areas and the vector of HLB, the Asian Citrus Psyllid (ACP), is present in all of the citrus producing areas of the state. Huge efforts are underway to prevent the devastation of California’s $7.2 billion citrus industry. According to the Citrus Research Board (CRB) California spent $40-45 million per year in the past three years in anti-ACP-HLB programs. A study commissioned by the CRB estimates a possible impact of a 20% reduction in California citrus acreage or yield or a combination of the two. This projected loss could result from increased costs to meet government regulations, combating the Asian citrus psyllid and warding off the invasion of HLB (Ref. #6). Such a reduction could cause a loss of 7,350 jobs and $127 million in employment income and could reduce California’s GDP by $501 million in direct, indirect and induced impacts. The CRB currently devotes most of its resources to battling ACP and HLB to help ensure the sustainability of California citrus (Ref. #6).
Impact of HLB in Florida
Florida was the site of the first report of HLB in 2005 and the effects have been devastating. They range from a 25% decrease in the number of orange trees in the state, an almost 50% reduction in the number of citrus bearing acres to an over 60% reduction in the number of grapefruit trees, growers and juice processing facilities and packing houses. The real cultural cost to manage HLB in orange groves for juice production in Florida is estimated to be $663 per acre, which represents a 67% increase compared to pre-HLB levels. However, and perhaps more importantly, the real cultural cost of production per box increased by 283% (Ref. #7).
Effects of HLB on Florida
Number of Grapefruit trees *
Number of Orange trees *
Number of Packing houses +
Number of Juice processing facilities +
Number of Citrus growers *
Number of Citrus bearing acres *
Sources: *U.S. Department of Agriculture-National Agricultural Statistics Service. + Florida Department of Agriculture & Consumer Services
Impact of HLB in Texas and Arizona
The Texas citrus industry has a statewide economic impact of over $280 million. Following the first report of HLB in Florida in 2005, efforts were made to implement state and federal quarantine measures to prevent the movement of potentially infected plant materials. The measures included the transition from open-field to enclosed nursery systems, the implementation of an area-wide psyllid control, surveys for HLB and ACP in commercial groves and residential sites, and removal of confirmed infected trees. Despite these efforts, HLB detection sites in Texas increased to 26% and 40% of commercial groves and residential sites, respectively, by 2017 (Ref. #9). Such a rapid disease progress despite efforts and investment to slow the disease spread underscores the enormous challenges posed by HLB once introduced into a new area.
At present, Arizona remains ACP infested but with no HLB finds.