http://www.weeklytimesnow.com.au/article/2009/11/18/133335_horticulture.html

Citrus disease warning

Sandra Godwin
November 18, 2009


Stripped: citrus trees being bulldozed in Queensland
as part of the citrus canker eradication program

THE 2004 outbreak of citrus canker in central Queensland convinced the industry of the importance of taking biosecurity seriously.

The disease cost growers more than $100 million, with 490,000 commercial trees, 4000 backyard trees and 150,000 native citrus trees bulldozed and burned as part of the eradication program.

But Citrus Australia technical adviser Pat Barkley warned delegates at last week's national citrus conference at Mildura the industry was vulnerable to an even more devastating disease, huanglongbing, also known as citrus greening.

A highly destructive bacterial disease, it is transmitted by psyllid insects or by using contaminated grafting material, and cannot be treated or cured, dramatically affecting productivity and killing trees within a few years.

Mrs Barkley said the psyllid vector and HLB, which was wiping out citrus industries in Brazil and Florida, had been found in East Timor, Indonesia and northern Papua New Guinea.

And Australia was especially vulnerable because of the widespread occurrence of native citrus, such as desert lime, coastal finger limes and popular garden plant orange jasmine.

"Awareness is the key to eradication," she said.

"Finding it early is important.

"If it was introduced into a Sydney suburb, it would spread like wildfire because it's got a host in orange jasmine."

Mrs Barkley said the disease could be transmitted through the illegal importation of budwood, legal imports of material that had not been properly inspected and treated, or by insects borne in cyclones or on planes.

While the psyllid itself was easy enough to identify, she said symptoms of HLB could be mistaken for nutritional disorders and other conditions, such as Australian citrus dieback.

The main symptom was asymmetric dull, blotchy mottling of leaves, which could be accompanied by small, lopsided fruit, and greening of the skin.

Biosecurity Services Group plant biosecurity general manager Louise van Meuers said the likelihood of psyllids on fruit imported from California was low but the Federal Government had imposed emergency measures since the discovery of the insects in four countries in the past year.

"We have AQIS inspectors in the US, where the season is about to start," she said.

Also during the conference, Plant Health Australia chief executive officer Greg Fraser launched a new Orchard Biosecurity Manual for citrus growers and an updated Citrus Industry Biosecurity Plan.

The manual is designed to help growers protect their orchards by regularly checking plant material, making workers aware of biosecurity measures and cleaning vehicles and equipment.