California: Citrus Trees Threatened by Greening Disease


B. McPherson

 

California is the latest state to be hit with the invasive fly that carries what is called Greening Disease. It was first identified in March of 2012 and has citrus growers on high alert. The culprit spreading the disease is a tiny flying insect, a psyllid fly. It has established itself in Florida where it was discovered in the citrus groves in 1998. Now California is fighting the difficult battle against this unwelcome pest from Asia.

The fly damages the citrus tree in two ways. It sucks juices from the new growth, leading to stunted and deformed growth. More seriously, it carries a bacterium that causes the greening disease. There is no treatment and no cure. Citrus trees must be cut down and destroyed to slow the spread of the disease. Once they are infected with Candidatus liberbacter, they are doomed in any case. Once infected any fruit produced is deformed, small and has a bad taste.

Humans have aided the spread of the disease as well. The 1998 infestation was discovered originating in commercial nursery plants. As well, Texas has sourced the pest to nursery stock. Transferring grafts from an infected tree to a non-infected one will also spread the disease. 

Florida orchardists have used pesticides to prevent infection of their trees. A systemic poison, Admire(imidacloprid) is used. Also neonicotinoids and pyrethroids may be applied. Florida has imported and released two parasitic wasps to try to control the flies. Ladybugs have proved to be voracious eaters of the insects as well.

This multi-million dollar invasive species has spread around much of the tropical and sub-tropical fruit growing areas. Australia and the Mediterranean are the only citrus growing areas without it.

Next time you return from an overseas trip and are asked to declare plant or animals material that you might be bringing with you, cooperate and tell the truth. The cost to growers and ranchers from introduced pests is enormous. If you don’t care about the producers, big or small, think about your own pocketbook. If California and Florida lose many of their citrus trees to this latest invader, your food bill will be greater.

For detailed information on the psyllid fly, the Universityof California has an excellent page.

Other names for Greening Disease: Huanglonglbing, yellow dragon disease

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