CitrusEditorial_v9

Remember when I wrote about Panama disease, the fungal blight which is coming for the Cavendish bananas (after laying waste to the Gros Michel cultivar bananas back in the 50s)?  Well, sadly, Panama disease is not the only apocalyptic fruit blight on the international circuit these days.  It turns out that a bacterial disease is destroying citrus groves around the United States and beyond.  The disease, known in English as “citrus wasting disease” is caused by a motile bacteria, Candidatus Liberibacter, which is spread by the Asian citrus psyllid (Diaphorina citri), an inconsequential Hemipteran insect which lives in citrus groves.  There are multiple strains of greening disease, and there have been for a long time, but the newly problematic strain originated in China where it is known by the evocative name “huánglóngbìng” which means “Yellow Dragon Disease.”

A revolting Asian citrus psyllid, Diaphorina citri

A revolting Asian citrus psyllid, Diaphorina citri

The wild ancestors of most of today’s grape fruits, oranges, and lemons, came originally from the forests of East and South East Asia so it is not a huge surprise that this horrible disease comes from there too.  Unfortunately hemipteran insects can easily proliferate in new ecosystems, so the disease became a problem after these invasive insect pests gained a widespread foothold throughout the semi-tropical regions where citrus is grown.

A tree infected with citrus greening disease

A tree infected with citrus greening disease

Citrus fruit is delicious and wonderful beyond compare…so it is worth big money.  This means that agricultural scientists have been studying huánglóngbìng and attempting to stymy it with medicines, pesticides, and transgenic tinkering.   The scientists themselves have been hampered in their research by the fact that it is hard to maintain and study citrus plants infected with the disease because they die so swiftly (the infected citrus plants, not the agricultural scientists).  Powerful antibiotics work to wipe out the disease, but it is not practical to give these medicines to trees (though we will probably try—with predictable results).  Scientists feel that there may be a transgenic solution, but it is unclear how marketable such a chimera will be (since protectionists and Luddites have been fear-mongering pretty hard against GMOs).

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This leaves mass application of insecticide as the best bulwark against huánglóngbìng.  It is starting to seem that small orchards and groves which are unwilling to commit to this kind of regimen will soon be gone.  All of this strikes me as unbearably sad and frightening.  Why are there so many blights everywhere?  Has this always been a peril of agriculture (indeed of life?) or has contemporary monoculture paved the way for widespread proliferation of these superbugs?  There must be some parasitoid wasp or something which has kept these damn psyllids from wiping out species citruses of wild Asia.  Maybe we could bring that here…but it probably would cause some new horrible problem.

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We’ll keep you posted.  In the meantime you should glut yourself on oranges this winter…while you still can.