Citrus greening - everything you need to know

citrusgreeningblog

Over the past 10 to 12 years, there has been a significant decrease in citrus crop sizes. One of the predominant causes is citrus greening (also known as huánglóngbìng or HLB) - a serious bacterial disease that affects the vascular systems of citrus trees, limiting nutrient uptake. The disease is vectored and transmitted by an insect, the Asian Citrus Psyllid. While it only causes minor damage to young shoots, it is the bacteria it passes on to the citrus trees that leads to greening symptoms and ultimately the tree’s death.

The disease poses no threat to humans or animals but has multiple detrimental effects to citrus groves including reduced yield, reduced fruit size and quality, discolouration of fruit and increases in the production costs. Once a tree is infected there is currently no cure.

Where did it originate?

There are two different types of HLB currently known. The first and by far most destructive form, the Asian strain Candidatus Liberibacter asiaticus (Ca. L., Las), was identified in China in 1943. In 1947, a second heat-sensitive form was discovered in South Africa. The Asian strain was discovered in Florida in 2005, where unfortunately it spread to virtually every citrus farm in less than two years. It has also impacted Brazilian citrus since 2004 when researchers first detected the disease in the southeastern part of the country.

The impact

Since greening was discovered in the Autumn of 2005 it has had devastating affects world-wide. Taking the Florida orange crop as an example, the most recent crop stands at a decline of over 70 percent from the 242 million boxes recorded in the 2003-04 season. Florida is the largest orange-producing state in the United States, and the third largest orange producer in the world behind Brazil and China. Approximately 95% of all oranges grown in Florida are processed for juice according to USDA /NASS.

What is being done to battle it?

Though millions of dollars are being spent annually on dramatic efforts to cure HLB, there is no proven cure and no resistant citrus varieties currently available to withstand the disease. Management is difficult but there are strategies available that aim to slow the spread of the disease. These include removing infected trees, planting new disease-free stocks in nurseries, psyllid management and promoting root health.

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